U.S. patent number 7,597,434 [Application Number 11/694,551] was granted by the patent office on 2009-10-06 for ink-jet apparatus and method of the same.
This patent grant is currently assigned to Toshiba Tec Kabushiki Kaisha. Invention is credited to Hideaki Nishida, Noboru Nitta, Masashi Shimosato, Isao Suzuki.
United States Patent |
7,597,434 |
Nitta , et al. |
October 6, 2009 |
Ink-jet apparatus and method of the same
Abstract
"Energy per unit volume" P2(Pa) generated in ink 4 in a second
ink tank 14 is maintained to the condition
"P2={(1+r).times.Pn}-(r.times.P1)" based on "energy per unit
volume" P1(Pa) generated in ink 4 in the first ink tank 12, a
proportion of "1:r" between channel resistance R1 (Pasec/m.sup.3)
of ink from the first ink tank 12 to the neighborhood of a nozzle 1
and channel resistance R2 (Pasec/m.sup.3) of ink from the
neighborhood of the nozzle 1 to the second ink tank 14, and
appropriate pressure Pn (Pa) of the ink 4 in the neighborhood of
the nozzle 1.
Inventors: |
Nitta; Noboru (Tagata-gun,
JP), Shimosato; Masashi (Izunokuni, JP),
Nishida; Hideaki (Izunokuni, JP), Suzuki; Isao
(Mishima, JP) |
Assignee: |
Toshiba Tec Kabushiki Kaisha
(Tokyo, JP)
|
Family
ID: |
38647898 |
Appl.
No.: |
11/694,551 |
Filed: |
March 30, 2007 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20070252860 A1 |
Nov 1, 2007 |
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Foreign Application Priority Data
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Apr 27, 2006 [JP] |
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2006-123927 |
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Current U.S.
Class: |
347/89; 347/7;
347/85 |
Current CPC
Class: |
B41J
2/175 (20130101); B41J 2/17509 (20130101); B41J
29/377 (20130101); B41J 2/17566 (20130101); B41J
2/17596 (20130101); B41J 2/17556 (20130101) |
Current International
Class: |
B41J
2/18 (20060101) |
Field of
Search: |
;347/5-7,9,85,89,92 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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55-121074 |
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Sep 1980 |
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JP |
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2000-289222 |
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Oct 2000 |
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JP |
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2005-161633 |
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Jun 2005 |
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JP |
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Primary Examiner: Nguyen; Lam S
Attorney, Agent or Firm: Turocy & Watson, LLP
Claims
What is claimed is:
1. An ink-jet apparatus comprising: at least one ink jet head that
includes a pressure chamber communicating with a nozzle and ejects
ink communicating with the pressure chamber from the nozzle; a
first pressure source that contains ink and generates, to the ink,
"energy per unit volume" P1 (Pa) that is based on static ink under
atmospheric pressure at a height position of an opening of the
nozzle; a second pressure source that contains ink and generates,
to the ink, "energy per unit volume" P2 Pa) that is based on static
ink under atmospheric pressure at the height position of the
opening of the nozzle, and control means, wherein the first
pressure source, the pressure chamber, and the second pressure
source are sequentially connected to a first channel and a second
channel, and assuming that a proportion of a first channel
resistance R1 of the first channel from a branching point to the
first pressure source to a second channel resistance R2 of the
second channel from the branching point to the second pressure
source is "1:r" wherein r=R2/R1, the branching point branches from
the first and second channels to the nozzle, the control means
maintains the "energy per unit volume" P2 (Pa) in a relationship of
"P2={(1+r).times.Pn}-(r.times.P1)" for at least an ink-ejecting
time from the nozzle, where the Pn is appropriate pressure of ink
near the opening of the nozzle.
2. The apparatus according to claim 1, wherein the appropriate
pressure Pn (Pa) is for maintaining a meniscus shape that a surface
of ink at the opening of the nozzle curves inside the opening.
3. The apparatus according to claim 1, wherein the appropriate
pressure Pn (Pa) falls within 0 (Pa) to -3000 (Pa).
4. The apparatus according to claim 1, wherein loss of the "energy
per unit volume" of ink caused by the channel resistances of the
first and second channels exceeds 3000 (Pa) during said at least
ink-ejecting time from the nozzle.
5. The apparatus according to claim 1, wherein; when the "energy
per unit volume" P1 and the "energy per unit volume" P2 are set to
different values to each other and ink is caused to flow between
the first pressure source and the second pressure source through
the first and second channels at a flow rate Q (m.sup.3/sec), the
control means controls the "energy per unit volume" P1 to the
condition of "P1=QR/(1+r)+Pn", based on a total channel resistance
R (Pasec/m.sup.3) of the first and second channels, viewed from the
first pressure source and the second pressure source, the flow rate
Q, the proportion "1:r", and the appropriate pressure Pn (Pa) of
ink near the opening of the nozzle.
6. The apparatus according to claim 1, wherein the ink jet head
includes a plurality of the nozzles, a first ink port nearer the
first pressure source from each branching point that branches from
the first and second channels to each nozzle, and a second ink port
nearer the second pressure source from each branching point, and
respective proportions of respective channel resistances from said
respective branching points to the first ink port and respective
channel resistances from said respective branching point to the
second ink port are equal to one another.
7. The apparatus according to claim 1, wherein a plurality of the
ink jet heads are provided, and respective proportions of
respective channel resistances, to the first pressure source, from
respective branching points that branch from the first and second
channels to the nozzles of respective ink jet heads, and respective
channel resistances from the respective branching points to the
second pressure source are equal to one another and are "1:r".
8. The apparatus according to claim 1, wherein the first pressure
source is a first ink tank having a first ink liquid level; the
first ink tank includes a first ink port and a second ink port; the
second pressure source is a second ink tank having a second liquid
level; the second ink tank includes a third ink port and a fourth
ink port; the first ink port and the third ink port are connected
to the first and second channels; the second ink port and the
fourth ink port are connected to first ink feed means; the first
ink feed means conducts entrance and exit of the ink to the second
ink port and the fourth ink port such that a detection result
obtained by a first liquid level sensor that detects a height of
the first ink liquid level, and a detection result obtained by a
second liquid level sensor that detects a height of the second ink
liquid level respectively indicate predetermined heights; and
assuming that a pressure at the first ink liquid level is Pi1 (Pa),
a pressure at the second ink liquid level is Pi2 (Pa), a height of
the first ink liquid level based on the height position of the
opening of the nozzle is h1(m), a height of the second ink liquid
level based on the height position of the opening of the nozzle is
h2(m), a density of the ink is .rho. (kg/m.sup.3), and a gravity
acceleration is g(m/s.sup.2), the "energy per unit volume" P1 and
the "energy per unit volume" P2 are "P1=Pi1+.rho.gh1" and
"P2=Pi2+.rho.gh2".
9. The apparatus according to claim 8, wherein the first ink liquid
level communicates with a first atmospheric pressure source that
has been subjected to pressure regulation; and the second ink
liquid level communicates with a second atmospheric pressure source
that has been subjected to pressure regulation.
10. The apparatus according to claim 9, further comprising: a pump
that can moves gas between the first atmospheric pressure source
and the second atmospheric pressure source, wherein a proportion of
a volume of the first atmospheric pressure source and that of the
second atmospheric pressure source is r:1.
11. The apparatus according to claim 8, wherein the first ink feed
means includes a second pump that can move ink between the first
ink tank and the second ink tank, wherein the first ink tank, the
first and second channels, the second ink tank, and the second pump
constitutes a circulating path that can circulate ink.
12. An apparatus according to claim 11, further comprising; a main
tank containing ink; and second ink feed means that performs
transportation and reception ink between the circulating path and
the main tank, wherein the second pump is controlled such that a
detection result obtained by the first liquid level sensor
indicates a predetermined height; and the second ink feed means is
controlled so that a detection result obtained by the second liquid
level sensor indicates a predetermined height.
13. The apparatus according to claim 12, wherein the second ink
feed means comprises a fourth ink channel connecting the main tank
and the circulating path, and a first pump provided in the fourth
ink channel, and feeds ink in a direction from the main tank toward
the circulating path while the detection result of the second
liquid level sensor is lower than the predetermined height and
feeds ink in a direction from the circulating path toward the main
tank while the second liquid level sensor is higher than the
predetermined height.
14. The apparatus according to claim 12, wherein "energy per unit
volume" P3 (Pa) of the main tank that is based on static ink under
atmospheric pressure at the height position of the opening of the
nozzle, the "energy per unit volume" P1, and the "energy per unit
volume" P2 satisfy a relationship of "P1>P3>P2", and the
second ink means comprises a fourth ink channel that communicates
with the main tank and is connected to the second ink tank, a first
valve for controlling connection and disconnection between the
second ink tank and the main tank, a fifth ink channel that
communicates with the main tank and is connected to the first ink
tank, and a second valve for controlling connection and
disconnection between the first ink tank and the main tank, opens
the first valve while the detection result of the second liquid
level sensor is lower than the predetermined height, and opens the
second valve while the detection result of the second liquid level
sensor is higher than the predetermined level.
15. The apparatus according to claim 8, wherein the first ink feed
means comprises a main tank containing ink; third ink feed means
that can move ink between the first ink tank and the main tank; and
fourth ink feed means that can move ink between the second ink and
the main tank, wherein the third ink feed means performs control
such that a detection result obtained by the first liquid level
sensor indicates a predetermined height; and the fourth ink feed
means performs control such that a detection result obtained by the
second liquid level sensor indicates a predetermined height.
16. The apparatus according to claim 8, wherein the first ink feed
means conducts entrance and exist of ink through the second ink
port and the fourth ink port, so that the detection result obtained
by the first liquid level sensor and the detection result obtained
by the second liquid level sensor coincide with the height position
of the opening of the nozzle, respectively.
17. The apparatus according to claim 8, wherein the first ink feed
means conducts entrance and exit of ink through the second ink port
and the fourth ink port such that the detection result obtained by
the first liquid level sensor and the detection result obtained the
second liquid level sensor satisfy "-Pn/(.rho.g)" based on the
height position of the opening of the nozzle.
18. The apparatus according to claim 8, wherein a pressure at the
first ink liquid level is atmospheric pressure; and the first ink
feed means conducts entrance and exit of ink through the second ink
port such that the liquid level height position detected by the
first liquid level sensor satisfies "P1/(.rho.g)" based on the
height position of the opening of the nozzle.
19. The apparatus according to claim 18, wherein a pressure of the
second ink liquid level is atmospheric pressure; and the first ink
feed means conducts entrance and exit of ink through the fourth ink
port such that the liquid level height position detected by the
second liquid level sensor satisfies "P2/(.rho.g)" based on the
height position of the opening of the nozzle.
20. The apparatus according to claim 8, further comprising: a
radiator that can exchange heat with external air, wherein the
first ink tank and the second ink tank together with the radiator
are arranged at an end of the apparatus that contacts with external
air.
21. The apparatus according to claim 8, wherein said at least one
ink jet head is arranged obliquely above the first ink tank, and
comprises a first supply pipe that supplies ink upwardly from the
first ink tank and has a thickness that enables air bubbles in the
ink to ascend together with the ink; a second supply pipe that
horizontally arranged above the first supply pipe, supplies ink
from the first supply pipe in a horizontal direction, and has a
sectional height that enables air bubbles in the ink to move
together with the ink; and a third supply pipe that supplies ink
from the second supply pipe to the ink jet head and has a thickness
that enables air bubbles in the ink to descend together with the
ink.
22. The apparatus according to claim 8, further comprising: a
decelerating mechanism that decelerates an ink flow rate and is
provided in an ink port of the first ink port and the second ink
port ink port in which ink flows.
23. The apparatus according to claim 22, wherein the decelerating
mechanism includes an isolating wall that isolates an area where
the ink port in which the ink in the first ink tank flows is
provided from an area where the other ink port is provided; an
upper edge of the isolating wall is longer than a perimeter of the
opening of the ink port in which the ink flows; and the ink spills
over from the upper end of the isolating wall to the area where the
other ink port is provided.
24. A method for controlling an ink-jet apparatus comprising: at
least one ink jet head that includes a pressure chamber
communicating with to a nozzle and ejects ink communicating with
the pressure chamber from the nozzle; a first pressure source that
contains ink and generates, to the ink, "energy per unit volume" P1
(Pa) that is based on static ink under atmospheric pressure at a
height position of an opening of the nozzle; and a second pressure
source that contains ink and generates, to the ink, "energy per
unit volume" P2 (Pa) that is based on static ink under atmospheric
pressure at the height position of the opening of the nozzle,
wherein the first pressure source, the pressure chamber and the
second pressure source are sequentially connected to a first
channel and a second channel, the method comprising: when it is
assumed that a proportion of a first channel resistance R1 of the
first channel from a branching point to the first pressure source
to a second channel resistance R2 of the second channel from the
branching point to the second pressure source is "1:r" wherein
r=R2/R1, the branching point branches from the first and second
channels to the nozzle, where the Pn is an appropriate pressure of
ink near the opening of the nozzle, maintaining the "energy per
unit volume" P2 (Pa) to a relationship of
"P2={(1+r).times.Pn}-(r.times.P1)" for at least an ejecting time
from the nozzle.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority
from the prior Japanese Patent Application No. 2006-123927, filed
Apr. 27, 2006, the entire contents of which are incorporated herein
by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink jet apparatus that
circulates ink through an ink jet head and ejects ink from nozzles
of the ink jet head, and a control method thereof.
2. Description of the Related Art
Conventionally, the ink jet apparatus that circulates ink through
an ink jet head and ejects ink from nozzles of the ink jet head has
been known. For example, there are the ink jet apparatuses
described in US 2002/0118256A1 and US 2005/0007399A1.
It is important for such an ink jet apparatus that the pressure of
ink at the neighborhood of nozzle openings of the ink jet head
should be always maintained at a constant level.
The ink jet apparatus described in US 2002/0118256A1 has a problem
that although the pressure of ink at the neighborhood of nozzle
openings largely depends on channel resistance of the pipeline
between an ink tank and the ink jet head, the pressure of ink at
the neighborhood of the nozzle openings is not constant because no
consideration is given to the channel resistance.
On the one hand, the ink jet apparatus described in US
2005/0007399A1 comprises a pressure reference. Liquid level control
is difficult for the pressure reference. Furthermore, there is a
problem that since a large quantity of ink should be supplied to
the pressure reference by a pump, the pump consumes much energy to
operate.
An object of the present invention is to provide an ink jet
apparatus that can always maintain the pressure of ink at the
neighborhood of nozzle openings at an appropriate pressure without
requiring complicated control and without involving considerable
energy consumption.
BRIEF SUMMARY OF THE INVENTION
An ink jet apparatus of the present invention comprises:
at least one ink jet head having a pressure chamber communicated to
nozzles and ejecting ink from the nozzles communicated to the
pressure chamber;
a first pressure source containing ink, and generating "energy per
unit volume" P1 (Pa) based on static ink of atmospheric pressure at
height position of openings of the nozzles;
a second pressure source containing ink, and generating "energy per
unit volume" P2 (Pa) based on static ink of atmospheric pressure at
height position of openings of the nozzles; and
a control means,
wherein the first pressure source, the pressure chamber, and the
second pressure source are sequentially connected by first and
second channels.
Given that a ratio of channel resistance of the channel to the
first pressure source from a branching point that branches from the
first and second channels to the nozzles, versus channel resistance
of the channel from the branching point to the second pressure
source is set as "1:r", the control means keeps the "energy per
unit volume" P2 (Pa) in accordance with the relation
P2={(1+r).times.Pn}-(r.times.P1) at least when ejecting ink from
the nozzles.
The Pn represents an appropriate pressure of ink at the
neighborhood of the nozzle openings.
Additional objects and advantages of the invention will be set
forth in the description which follows, and in part will be obvious
from the description, or may be learned by practice of the
invention. The objects and advantages of the invention may be
realized and obtained by means of the instrumentalities and
combinations particularly pointed out hereinafter.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
The accompanying drawings, which are incorporated in and constitute
a part of the specification, illustrate presently preferred
embodiments of the invention, and together with the general
description given above and the detailed description of the
preferred embodiments given below, serve to explain the principles
of the invention.
FIG. 1 is a section view showing the internal structure of an ink
jet head of first to seventh embodiments.
FIG. 2 is a view showing the configuration of the first
embodiment.
FIG. 3 is a view showing the configuration of the second
embodiment.
FIG. 4 is a view showing the configuration of the third
embodiment.
FIG. 5 is a view showing the configuration of the fourth
embodiment.
FIG. 6 is a view for illustrating pressure control of fourth
embodiment.
FIG. 7 is a view showing the configuration of the fifth
embodiment.
FIG. 8 is a view showing a position of combined channel resistance
Rt1 in FIG. 7.
FIG. 9 is a view showing a position of combined channel resistance
Rt2 in FIG. 7.
FIG. 10 is a view showing a position of combined channel resistance
Rt6 in FIG. 7.
FIG. 11 is a view showing a specific configuration in a first ink
channel and a second ink channel of the fifth embodiment.
FIG. 12 is a view showing a spreadsheet in the fifth
embodiment.
FIG. 13 is a view showing each operation pattern in the fifth
embodiment.
FIG. 14 is a view showing a specific configuration of a radiator
and the periphery thereof in the fifth embodiment.
FIG. 15 is a view showing a configuration of a substantial part of
the sixth embodiment.
FIG. 16 is a view showing a configuration of a substantial part of
the seventh embodiment.
FIG. 17 is a view showing the internal structure of the ink jet
head of the eighth embodiment.
FIG. 18 is an equivalent circuit schematic for illustrating
proportional distribution of the channel resistance set forth in
the fifth embodiment.
DETAILED DESCRIPTION OF THE INVENTION
[1] FIRST EMBODIMENT
In the following, a first embodiment of the present invention will
be described with reference to the drawings.
FIG. 1 shows a cross section of an ink jet head 11 of an ink
circulating type. That is, a pressure chamber 3 is formed on a top
surface side of an orifice plate 2 having a nozzle 1 for ejecting
ink. Formed as a middle part of a channel 5 in the head which ink 4
runs through is narrowed, the pressure chamber 3 not only has the
above-mentioned nozzle 1, but also has an actuator 6 on the surface
side opposed to the nozzle 1. The ink 4 runs from right to left as
shown in the figure, through the pressure chamber 3, in the channel
5 within the head.
As the actuator 6 is driven, the ink 4 within the pressure chamber
3 forms an ink droplet 4a and is ejected from the nozzle 1. As the
actuator 6, those directly or indirectly transforming the pressure
chamber 3 by use of a piezoelectric device such as a PZT are known.
Furthermore, as the ink jet head, any of those driving a diaphragm
by static electricity, those heating ink by a heater and producing
air bubbles to generate pressure, those directly moving ink 4 by
static electricity, and like may be used. The position where the
actuator 6 is to be provided is not limited to the surface side
opposed to the nozzle 1, but may be a surface located in the depth
direction of the figure, for example. In addition, the ink 4 in the
pressure chamber 3 is not necessarily to be ejected from the nozzle
1 directly, and the pressure chamber 3 may be communicated with the
nozzle 1 so that the ink 4 is ejected from the nozzle 1 when the
actuator 6 is driven for generating pressure in the pressure
chamber 3.
FIG. 2 shows the overall configuration.
A first ink tank 12 serving as a first pressure source is provided.
The first ink tank 12 not only contains the ink 4 for supply to the
pressure chamber 3 in the ink jet head 11, but also additionally
comprises a first atmospheric pressure source 12a and generates to
the ink 4 "energy per unit volume" P1 (Nm/m.sup.3) that is based on
static ink of atmospheric pressure at the height position of an
opening of the nozzle 1. The unit Nm/m.sup.3 is equal to Pascal
(Pa). This "energy per unit voltage" P1 (Pa) refers to the "energy
per unit volume" of the "Bernoulli equation" and a sum (value) of
static pressure, dynamic pressure and potential pressure. In the
following description, unless otherwise specified, a reference
height of the potential pressure shall be a height position of the
opening of the nozzle 1, and a reference of the "energy per unit
volume" shall be static ink of atmospheric pressure at the height
position of the opening of the nozzle 1.
When dynamic pressure can be ignored, "energy per unit volume" P1
is expressed as a sum (value) "Pi1+.rho.gh1" of static pressure Pi1
of the ink 4 at liquid level within a first ink tank 12 and
potential pressure ".rho.gh1" of the ink 4 at liquid level within
the first ink tank 12. .rho.(kg/m.sup.3) is density of the ink 4.
g(m/s.sup.2) is gravity acceleration rate of the ink 4. h1(m) is a
height position at the liquid level of the ink 4 within the first
ink tank 12 based on the height position of the opening of the
nozzle 1, i.e., a so-called potential head. As described later, in
this embodiment, as control is exercised so that "h1=0", it is
"Pi1=P1".
The ink 4 within the first ink tank 12 is guided into an inflow ink
port of the ink jet head 11 by a first ink channel 13a. The guided
ink 4 runs through the pressure chamber 3 of the ink jet head 11
and flows out from an outflow ink port into a second ink channel
13b. The ink 4 flowing out into the second ink channel 13b is
guided to a second ink tank 14 that is a second pressure
source.
The second ink tank 14 receives the ink 4 flowing out from the
pressure chamber 3 of the ink jet head 11, and additionally
comprises a second atmospheric pressure source 14a, which generates
an "energy per unit volume" P2 (Pa) within the ink 4.
When dynamic pressure can be ignored, the "energy per unit volume"
P2 is expressed as a sum (value) "Pi2+.rho.gh2" of static pressure
Pi2 of the ink 4 at the liquid level within the second ink tank 14
and potential pressure ".rho.gh2" at the liquid level of the ink 4
within the second ink tank 14. h2(m) is a height position at the
liquid level of the ink 4 within the second ink tank 14 that is
based on a height position of the opening of the nozzle 1, i.e.,
potential head. As described later, in this embodiment, as control
is exercised so that "h2=0", it is "Pi2=P2".
Here, a supplementary explanation of "energy per unit volume" of
the "Bernoulli equation" of the ink 4 in the first ink tank 12 is
given.
As described earlier, the pressure of the ink 4 at the liquid level
within the first ink tank 12 and the "energy per unit volume" of
the "Bernoulli equation" are both P1(=Pi1).
In addition, the potential pressure of the ink 4 at the liquid
level within the first ink tank 12 is 0.
Next, the "energy per unit volume" of the "Bernoulli equation" of
ink 4 at a location that is x deep under the liquid level within
the first ink tank 12 is considered. The pressure of the ink 4 at
the location that is just x(m) deep under the liquid level is
"P1+.rho.gx", which is just ".rho.gx" higher than the pressure at
the liquid level. On the one hand, the potential pressure of the
ink 4 at a location that is just x deep under the liquid level
decreases from that at the liquid level by ".rho.gx", and is
"-.rho.gx". Therefore, by summing the "P1+.rho.gx" and "-.rho.gx",
the "energy per unit volume" of the "Bernoulli equation" of the ink
4 at the location just x deep under the liquid level is
"P1+.rho.gx-.rho.gx=P1". Thus, the "energy per unit volume" at the
location that is just x deep under the liquid level does not differ
from that at the liquid level. This is because by being x deep
under the liquid level, the potential energy is simply replaced by
pressure energy, and the total amount of energy does not change.
The "energy per unit volume" of the "Bernoulli equation" of the ink
4 within the first ink tank 12 has been described above, but the
description also applies to the "energy per unit volume" of the
"Bernoulli equation" of the ink 4 within the second ink tank 14. In
general, when channel resistance within a container and kinetic
energy of ink can be ignored, because of "Bernoulli's theorem" the
"energy per unit volume" of the "Bernoulli equation" of ink within
the container is uniform everywhere within the container,
irrespective of how deep it is from the liquid level. Therefore,
ink within this container can be considered a pressure source that
generates the "energy per unit volume" of the "Bernoulli
equation".
For example, if an attempt to eject ink by connecting a flexible
tube to the container is made, the pressure to be applied to the
mouth of the tube varies depending on a height position of the
ejection port to be connected. However, the potential pressure of
the mouth of the tube varies by the same amount as the pressure,
but in a reverse relationship. Thus, if the negative load from the
tube of attempting to eject ink remains unchanged, the flow of ink
running into the tube is the same, from whatever height position of
the container ink is ejected, and is thus determined by the "energy
per unit volume" of the "Bernoulli's equation" of the ink within
the container and the negative load from the tube.
A third ink channel 13c is provided between the second ink tank 14
and the first ink tank 12. In a second pump 17 and a filter 18 are
provided in the third ink channel 13c, and the ink 4 is fed to the
first ink tank 12 by operation of the second pump 17. The filter 18
removes foreign matter mixed into the ink 4 running through the
third ink channel 13c.
The first ink tank 12, the first ink channel 13a, the ink jet head
11, the second ink channel 13b, the second ink tank 14, the third
ink channel 13c, the second pump 17, and the filter 18 form a
circulating path for the ink 4.
Further, a main tank 15 in which the ink 4 is contained and which
is opened to the atmospheric pressure is provided. A fourth ink
channel 13d is provided between this main tank 15 and the third ink
channel 13c (side closer to the second ink tank 14).
A first liquid level sensor 19 is provided in the first ink tank 12
to detect a height position of the liquid level of the ink 4
therein. A second liquid level sensor 20 is provided in the second
ink tank 14 to detect a height position of the liquid level of the
ink 4 therein. Detection results by these liquid level sensors 19,
20 are supplied to CPU 10.
A first pump 16 is provided in the fourth ink channel 13d. The
first pump 16 is controlled by CPU 10 to increase or decrease an
amount of the ink 4 within the circulating path so that a height
position detected by the second liquid level sensor becomes equal
to that of the opening of the nozzle 1 of the ink jet head 11. In
other words, while the height position detected by the second
liquid level sensor 20 is lower than that of the opening of the
nozzle 1 of the ink jet head 11, the ink 4 is fed to the
circulating path. While the height position detected by the second
liquid level sensor 20 is higher than that of the opening of the
nozzle 1 of the ink jet head 11, the ink 4 is returned to the main
tank 15 from the circulating path.
On the one hand, the second pump 17 is controlled by CPU 10 so that
a height position detected by the first liquid level sensor 19
becomes equal to that of the opening of the nozzle 1 of the ink jet
head 11. In other words, while the height position detected by the
first liquid level sensor 19 is lower than that of the opening of
the nozzle 1 of the ink jet head 11, the second pump 17 is
accelerated or driven. While the height position detected by the
first liquid level sensor 19 is higher than that of the opening of
nozzle 1 of the ink jet head 11, the CPU decelerates or stops the
second pump 17.
Thus, the liquid level of the ink 4 within the first ink tank 12
and that of the ink 4 within the second ink tank 14 are maintained
at the same height position as that of the opening of the nozzle 1
of the ink jet head 11.
The "energy per unit volume" P1 of the ink 4 within the first ink
tank 12 and the "energy per unit volume" P2 of the ink 4 within the
second ink tank 14 correspond to the atmospheric pressure of the
atmospheric pressure source 12a and that of the atmospheric
pressure source 14a. These atmospheric pressures are controlled by
CPU 10.
Here, if "P1>P2" is set, the ink 4 within the first ink tank 12
flows into the second ink tank 14 through the neighborhood of the
nozzle 1 of the pressure chamber 3 in the ink jet head 11. At the
same time, the ink 4 within the second ink tank 14 returns to the
first ink tank 12 through the third ink channel 13c, the second
pump 17 and the filter 18, thus circulating in the circulating
path.
In such an ink supply system that supplies ink to the ink jet head
11, dynamic pressures at any location within the circulating path
are small enough to be ignored. In addition, as the Reynolds number
at any location within the circulating path is also sufficiently
small, and effects of turbulent flow of the ink 4 can be
ignored.
In the following, a description of the case in which "ejected
amount per unit time" of the ink 4 in the nozzle 1 is sufficiently
small in comparison to the flow rate of the ink 4 in the pressure
chamber 3 will be continued. In this case, the pressure loss within
the ink jet head 11 and the ink supply system to the ink jet head
11 depends largely on the circulation flow rate rather than on the
ink ejection amount.
The flow Q(m.sup.3/sec) of the ink 4 flowing in the ink channel
that runs from the first ink tank 12 to the second ink tank 14
through the neighborhood of the nozzle 1 of the pressure chamber 3
is expressed in the following formula (1): Q=(P1-P2)/(R1+R2) (1)
wherein R1(Pasec/m.sup.3) is the channel resistance of the ink 4
from the first tank 12 to the neighborhood of the nozzle 1 in the
pressure chamber 3, and R2(Pasec/m.sup.3) is the channel resistance
of the ink 4 from the neighborhood of the nozzle 1 in the pressure
chamber 3 to the second ink tank 14.
In other words, the ink flow rate Q is determined by the channel
resistances R1, R2 and the difference between the "energy per unit
volume" P1 of the ink 4 within the first ink tank 12 and the
"energy per unit volume" P2 of the ink 4 within the second ink tank
14.
The channel resistances R1, R2 are decided by the viscosity of the
ink 4 and shape of the channel. Thus, to adjust the ink flow rate Q
to a predetermined value, the values of the "energy per unit
volume" P1, P2 will be adjusted. In fact, CPU 10 adjusts the values
of P1, P2 by adjusting either the atmospheric pressure of the
atmospheric pressure source 12a or atmospheric pressure of the
atmospheric pressure source 14a, or both of them, thereby obtaining
desired ink flow rate Q. For example, if the "energy per unit
volume" P1 is increased or the "energy for unit volume" P2 is
decreased, the ink flow rate Q can be increased. Conversely, the
ink flow Q can be decreased if the "energy per unit volume" P1 is
decreased or the "energy per unit volume" P2 is increased.
At the same time, CPU 10 maintains a relationship of "energy per
unit volume" P1, P2, as shown in the following formula (2), wherein
Pn is a constant. P2={(R1+R2)/R1}.times.Pn-(R2/R1).times.P1 (2)
When no ink 4 is ejected, the pressure (Pa) of the ink 4 in the
neighborhood of the opening of the nozzle 1 is "P2+Q.times.R2". If
the formulas (1) and (2) are substituted into the "P2+Q.times.R2",
the following formula (3) is developed:
.times..times..times..times..times..times..times..times..times..times..ti-
mes..times..times..times..times..times..times..times..times..times..times.-
.times..times..times..times..times..times..times..times..times..times..tim-
es..times..times..times..times..times..times..times..times..times..times..-
times..times..times..times..times..times..times..times..times..times..time-
s..times..times..times..times..times..times..times..times..times..times..t-
imes..times..times..times..times..times..times..times..times..times..times-
..times..times..times. ##EQU00001##
In other words, the constant Pn corresponds to the pressure (Pa) of
the ink 4 in the neighborhood of the opening of the nozzle 1, and a
value contained in the range of, for example, 0 (Pa) to -3000 (Pa)
is selected so that the surface of the ink at the opening of the
nozzle 1 retains a meniscus (refer to FIG. 1) curving to the inner
side of the opening. If the constant Pn is greater than 0 (Pa), the
ink 4 may leak from nozzle 1. If it is smaller than -3000 (Pa),
extra air may be sucked into the nozzle 1. In the following, the
constant Pn is referred to as the appropriate pressure of the ink 4
in the neighborhood of the opening of the nozzle 1.
While the ejection operation of the ink 4 is performed, the
pressure of the ink 4 in the neighborhood of the opening of the
nozzle 1 widely varies at high frequencies due to ejection.
However, when the ink 4 is ejected, the meniscus is intentionally
broken due to the ejection. Thus, the appropriate pressure Pn of
the ink 4 in the neighborhood of the opening of the nozzle 1 that
is to be maintained herein refers to a mean value excluding the
high frequency components due to the ejection operation, or
pressure during a pause between an ejection operation and a next
ejection operation.
Strictly speaking, the pressure of the ink 4 in the neighborhood of
the opening of the nozzle 1 is a value obtained by adding the
potential pressure attributable to a slight difference of
evaluation between the neighborhood of the nozzle 1 in the pressure
chamber 3 and the neighborhood of the opening of the nozzle 1, to
the pressure in the neighborhood of the nozzle 1 in the pressure
chamber 3.
If the relationship of channel resistances R1, R2 is "R1=R2", the
formula (2) of the "energy per unit volume" P2 is simpler, as shown
in the following formula (4): P2=2Pn-P1 (4)
In addition, if a proportion of the channel resistance R1 and
channel resistance R2 is expressed as "1:r" (in other words,
R2/R1=r), the formula (2) of the "energy per unit volume" P2 is as
shown in the following formula (5):
P2={(1+r).times.Pn}-(r.times.P1) (5)
In other words, the relationship of the "energy per unit volume" P1
and P2 for maintaining the appropriate pressure Pn of the ink 4 in
the neighborhood of the opening of the nozzle 1 is not influenced
by absolute values of the channel resistances R1, R2, and
determined only by the proportion of the channel resistance R1 and
the channel resistance R2 "1:r".
In the conventional ink jet apparatus, if the pressure loss
generated due to the channel resistance in a channel connecting a
pressure source and an ink jet head is high, it is difficult to
maintain the pressure of ink 4 in the neighborhood of an opening of
a nozzle 1 at an appropriate pressure. In particular, for example,
in the case in which the pressure loss generated by the channel
resistance in the channel connecting the pressure source and the
ink jet head (strictly speaking, loss of the "energy per unit
volume" of ink 4) accounts for more than half of the magnitude
(range) of the "range of the appropriate pressure of the ink 4 in
the neighborhood of the opening of the nozzle 1", in other words,
for instance, if a value obtained by multiplying the channel
resistance of the channel connecting the pressure source and the
ink jet head by flow rate of this channel exceeds 1500 (Pa), it is
quite difficult to keep the pressure of the ink 4 in the
neighborhood of the opening of the nozzle 1 at the appropriate
pressure. However, according to the present invention, the pressure
of the ink 4 in the neighborhood of the opening of the nozzle 1 is
not influenced by absolute values of the channel resistances R1,
R2, and is determined only by the proportion of the channel
resistance R1 and the channel resistance R2. Thus, even when the
pressure loss due to the channel resistance R1 and the channel
resistance R2 exceeds a total of 3000 (Pa), the pressure of the ink
4 in the neighborhood of the opening of the nozzle 1 can be
maintained at the appropriate pressure.
In addition, if the viscosity of the ink 4 changes due to a
difference in ambient temperatures, or a different kind of ink 4
having a different viscosity is used, the absolute values of the
channel resistances R1, R2 change. However, if the viscosity of the
ink 4 within the circulating path is uniform, the proportion of the
channel resistance R1 and the channel resistance R2 "1:r" is kept
constant as far as physical forms of the ink channels 13a, 13b
remain unchanged. In other words, if CPU 10 controls the
relationship of the "energy per unit volume" P1, P2 so that the
formula (5) can be maintained, the pressure in the neighborhood of
the nozzle 1 in the pressure chamber 3 can be kept constant even if
the ambient temperature or kind of ink 4 differs.
For example, when a cross-section area of the ink channel 13a in
the upstream side from the nozzle 1 is the same as that of the ink
channel 13b in the downstream side from the nozzle 1, a proportion
of the length of the ink channel 13a and that of the ink channel
13b corresponds to the proportion of the channel resistance R1 and
the channel resistance R2, namely "1:r", the "energy per unit
volume" P2 may be set based on the formula (5) that uses the
proportion. As a result, the pressure of the ink 4 in the
neighborhood of the opening of the nozzle 1 can be kept at the
appropriate pressure Pn.
Although the ink flow rate Q changes if the absolute values of the
channel resistances R1, R2 change, pressure changes or effects of
turbulent flow can be ignored if the dynamic pressure of the ink 4
running through the pressure chamber 3 is small and the Reynolds
number in the pressure chamber 3 is small. Thus, unless the ink
flow rate Q changes exponentially, a change in the ink flow Q does
not directly affect the ejection operation of the ink 4. In
contrast to this, the pressure of the ink 4 in the neighborhood of
the opening of the nozzle 1 directly affects the ejection operation
of the ink 4. Thus, keeping the pressure of the ink 4 in the
neighborhood of the opening of the nozzle 1 appropriate is more
important than keeping the ink flow rate Q, and is a condition to
be prioritized.
Nevertheless, when the ink flow rate Q varies too widely, problems
such as poor performance of a pump to be used or inadequate
capacity of an ink tank, and reduction of the homogenization effect
of ink temperatures or air bubble removal effect that are
advantages of circulation of ink 4 arise. Thus, to prevent a change
in the ink flow rate Q from becoming too substantial, the "energy
per unit volume" P1 of the first ink tank 12 may be corrected, with
respect to viscosity of the ink 4.
If the channel resistance proportion r and the constant Pn are used
in place of the "energy per unit volume" P2, the formula (1) that
expresses the ink flow rate Q is developed as shown in the
following formula (6):
.times..times..times..times..times..times..times..times..times..times..ti-
mes..times..times..times..times. ##EQU00002##
If "R1+R2" has increased as the viscosity of the ink 4 increased, a
change of the ink flow rate Q can be prevented by adjusting the
"energy per unit volume" P2 according to the formula (5), while the
"energy per unit volume" P1 is increased so that "P1-Pn" is
higher.
When the ink flow rate Q and all-channel resistance R, which is the
combined resistance of the channel resistances R1, R2 is used, the
"energy per unit volume" P1 to be given is expressed by the
following formula (7): P1=QR/(1+r)+Pn (7)
As the all-channel resistance R is proportional to viscosity of the
ink 4, a change in the ink flow rate Q can be prevented if the
"energy per unit volume" P2 is adjusted according to the formula
(5), while adjusting the "energy per unit volume" P1 depending on
the viscosity of the ink 4 by using this formula (7). For the
reasons that have already been mentioned, this adjustment does not
need to be so rigorous. In addition, regardless of whether this
adjustment was performed or not, the pressure of the ink 4 in the
neighborhood of the opening of the nozzle 1 can be kept at the
appropriate pressure Pn if a form of control to set the "energy per
unit volume" P2 according to any condition of the formulas (2),
(4), and (5) is adopted.
Although here the case in which the ink flow rate Q is adjusted by
increasing or decreasing the "energy per unit volume" P1, and the
"energy per unit volume" P2 is set so that the appropriate pressure
Pn can be obtained is described, on the contrary, the ink flow rate
Q may be adjusted by increasing or decreasing the "energy per unit
volume" P2, and the "energy per unit volume" P1 may be set so that
the appropriate pressure Pn can be obtained.
In the formulas (2), (4) and (5), a value of the "energy per unit
volume" P2 for obtaining the appropriate pressure of the ink 4 in
the neighborhood of the opening of the nozzle 1 is given as a
function of the "energy per unit volume" P1. Conversely, the
respective formulas may be solved for the "energy per unit volume"
P1, and a value of the "energy per unit volume" P1 for obtaining
the appropriate pressure of the ink 4 in the neighborhood of the
opening of the nozzle 1 may be given as a function of the "energy
per unit volume" P2. The point is that the relationship of the
"energy per unit volume" P1, P2 may satisfy any of the formulas
(2), (4), or (5).
In addition, it is possible to perform maintenance in which any
foreign matter, air bubble and the like present within the ink jet
head 11 may be pushed away to the downstream side by increasing the
"energy per unit volume" P1 and thereby increasing the ink flow
rate Q. With continued control for setting the "energy per unit
volume" P2 according to any of the conditions of the formulas (2),
(4), or (5) even during this, the pressure of the ink 4 in the
neighborhood of the opening of the nozzle 1 can be kept at the
appropriate pressure Pn. Therefore, during maintenance, neither ink
will leak from the nozzle 1 nor unwanted air will flow into the
nozzle 1. That is, economic and efficient maintenance is possible
without breaking the meniscus of the ink 4 at the opening of the
nozzle 1.
To wash away any foreign matter, air bubble and the like present
within the ink jet head 11 to the downstream side, the ink flow
rate Q may be as high as possible. However, if the highest ink flow
rate Q is maintained at all times, there are concerns that the life
of the pump 17 will be adversely affected, the pump 17 may generate
noise, the ink channels 13a, 13b, 13c may deteriorate, the filter
18 may deteriorate, the ink 4 may receive unwanted stress, air
bubbles may mix from any location of the ink channels 13a, 13b,
13c, and will be fed to the ink jet head 11 or the like. Thus, it
is desirable to increase the ink flow rate Q only when necessary.
In this embodiment, even if the ink flow rate Q is changed, the
pressure of the ink 4 in the neighborhood of the opening of the
nozzle 1 can be controlled to the appropriate pressure Pn. Thus,
such use (use in which the ink flow rate Q is increased only when
necessary) is possible.
In addition, in doing maintenance, the pressure of the ink 4 in the
neighborhood of the opening of the nozzle 1 may be set higher than
usually appropriate pressure on purpose, thereby the ink 4 is
forcibly ejected from the nozzle 1. This enables such operations as
wetting the periphery of the opening of the nozzle 1 with the ink
4, pushing out any foreign matter (including solidified ink 4)
present inside the opening of the nozzle 1 from the nozzle 1,
removing any foreign matter attached to the periphery of the
opening of the nozzle 1, etc.
When a plurality of ink jet heads 11 are incorporated, the
configuration can be such that the ink 4 is guided from the first
ink tank 12 respectively through a plurality of ink channels 13a
into respective ink jet heads 11, and then the ink 4 that has gone
through the respective ink jet heads 11 is guided respectively
through a plurality of ink channels 13b into the second ink tank
14. In this case, if each of the plurality of ink channels 13a
mutually has the same thickness and length and yet each of the
plurality of ink channels 13b mutually has the same thickness and
length, the flow rate of the ink 4 running through the plurality of
ink jet heads 11 and pressure of the ink 4 in the neighborhood of
the opening of the nozzle 1 can be matched, respectively.
However, in general, as ink jet heads 11 located closer to the
first ink tank 12 and the second ink tank 14 and ink jet heads 11
located far therefrom are mixed together, it is frequently
difficult to match the lengths of the plurality of ink channels 13a
or the lengths of the plurality of ink channels 13b.
In this case, if the channel resistances of the ink 4 from the
first ink tank 12 to the neighborhood of the nozzle 1 in the
pressure chamber 3 of the respective ink jet heads 11 are expressed
as R11, R12, R13, . . . , and the channel resistances of the ink 4
from the neighborhood of the nozzle 1 in the pressure chamber 3 of
the respective ink jet heads 11 to the second ink tank 14 are
expressed as R21, R22, R23, . . . , satisfying the condition of
"R21/R11=R22/R12=R23/R13= . . . " makes it possible to mutually
keep the pressure of the ink 4 at the same value in the
neighborhood of the opening of the nozzle 1 in the respective ink
jet heads 11, although the flow rates among the respective ink jet
heads 11 are not necessarily identical. At this time, with a
proportion of the channel resistance of the ink 4 from the first
ink tank 12 to the neighborhood of the nozzle 1 in the pressure
chamber 3 of the respective ink jet heads 11 and the channel
resistance from the neighborhood of the nozzle 1 in the pressure
chamber 3 of the respective ink jet heads 11 being
"R21/R11=R22/R12=R23/R13= . . . =r", if the relationship of P1, P2
is controlled according to the formula (2) or (5), or furthermore
if with the proportion being "r=1", the relationship of P1, P2 is
controlled according to the formula (4), it is possible to maintain
the appropriate pressure of the ink 4 in the neighborhood of the
opening of the nozzle 1 of each ink jet head 11.
An ink jet head 11 is not limited to that with one nozzle 1, and
those having a plurality of pressure chambers 3 and a plurality of
nozzles 1 that are arranged in a direction orthogonal to the flow
direction of the ink 4 (depth direction in FIG. 1) are also
possible. For an ink jet head 11 having a plurality of pressure
chambers 3 and a plurality of nozzles 1, if the channel resistances
from an inflow side ink port of the ink jet head 11 to the
neighborhood of the nozzles 1 in the respective pressure chambers 3
are expressed as Z11, Z12, Z13, . . . , and the channel resistances
from the neighborhood of the nozzle 1 in the respective pressure
chambers 3 to an outflow side ink port of the ink jet head 11 are
expressed as Z21, Z22, Z23, . . . , then, satisfying the condition
"Z21/Z11=Z22/Z12=Z23/Z13= . . . " makes it possible to keep the
pressure of the ink 4 in the neighborhood of the openings of the
respective nozzles 1 at mutually the same value.
So far the operations of the range when ink ejection amount per
unit time of the ink 4 in the nozzle 1 is sufficiently smaller than
the circulating flow and thus possible effect thereof can be
ignored are reviewed. If the effect of the ink ejection amount per
unit time cannot be ignored, however, the effect of the ink
ejection amount per unit time may be combined with the
configuration.
In other words, when pressure fluctuations against ejection flow
rate of the ink supply system are considered, it can be thought
that this ink supply system is equivalent to a supply system that
supplies through the channel resistances "(R1.times.R2)/(R1+R2)"
that is parallel resistances of the channel resistances R1, R2 from
the pressure source of the appropriate pressure Pn. Thus, when the
ink 4 is ejected from the nozzle 1, the pressure of the ink 4 in
the neighborhood of the opening of the nozzle 1 becomes larger than
the appropriate pressure Pn by the pressure loss generated by the
ink 4 running through the parallel resistances of the channel
resistances R1, R2. Hence, absolute values of the channel
resistances R1, R2 may be set to such a degree that this pressure
loss can be allowed for.
However, as the pressure loss due to the channel resistance from
the neighborhood of the nozzle 1 of the pressure chamber 3 to the
neighborhood of the opening of the nozzle 1 is usually considered
when operations of the actuator 6 are set for ejection, it is not
considered herein.
In addition, so far it has been described that the dynamic pressure
due to flow of the ink 4 in the vicinity of the nozzle 1 cannot be
ignored. However, to be more exact, the current velocity of the ink
4 in the vicinity of the nozzle 1 may be calculated, and the
appropriate pressure Pn may be increased by pressure drop due to
dynamic pressure of this current velocity.
As described above, it is possible to always keep the pressure of
ink 4 in the neighborhood of an opening of a nozzle 1 at
appropriate pressure Pn, irrespective of a change of the ink flow
rate Q and without requiring complicated control or considerable
energy consumption.
[2] SECOND EMBODIMENT
When ink 4 circulates in the direction from the first ink tank 12
through the head to the second tank 14, the condition P1>P2
exists. If the "energy per unit volume" of the ink 4 within the
main tank 15 lies between the "energy per unit volume" P1 and
"energy per unit volume" P2, the ink supply system can be
simplified by adopting a fifth ink channel 22, a first valve 21,
and a second valve 23 in place of the first pump 16, as shown in
FIG. 3.
The fifth ink channel 22 is provided between a region on the side
closer to the first ink tank 12 of the third ink channel 13c and
the fourth ink channel 13d.
The connecting point of the fifth ink channel 22 and the third ink
channel 13c is provided in a location sufficiently close to the
first ink tank 12. At this time, the "energy per unit volume" of
the ink at the connecting point then can be considered as almost at
P1.
The connecting point of the fifth ink channel 22 and the fourth ink
channel 13d is provided in a location sufficiently close to the
second ink tank 14. At this time, the "energy per unit volume" of
the ink at the connecting point then can be considered as almost at
P2.
The first valve 21 is provided at the connecting position of the
third ink channel 13c in the fourth ink channel 13d and the
connecting position of the fifth ink channel 22. The second valve
23 is provided in the fifth ink channel 22. Then, controlled by CPU
10, the first valve 21 and the second valve 23 increase or decrease
an amount of the ink 4 in the circulating path, so that a height
position detected by the second liquid level sensor 20 (a height
position of the liquid level of the ink 4 within the second ink
tank 14) is the same as a height position of the opening of the
nozzle 1 of the ink jet head 11.
Similarly to the first embodiment, the second pump 17 is controlled
according to a height position of the liquid level of the ink 4
within the first ink tank 12 that is detected by the first liquid
level sensor 19.
If the height position of the liquid level of the ink 4 within the
second ink tank 14 detected by the second liquid level sensor 20 is
lower than the height position of the opening of the nozzle 1 of
the ink jet head 11, the valve 21 is opened to replenish ink 4 to
the second ink tank 14.
On the one hand, if the height position of the liquid level of the
ink 4 within the second ink tank 14 detected by the second liquid
level sensor 20 is higher than the height position of the opening
of the nozzle 1 of the ink jet head 11, the valve 23 is opened to
suck out the ink 4 from the first ink tank 12. At that time, in
doing so, although the liquid level of the ink 4 within the first
ink tank 12 descends once, the second pump 17 is then actuated to
return the liquid level of the ink 4 within the first ink tank 12.
Simultaneously the liquid level of the ink 4 within the second ink
tank 14 descends.
Thus, similarly to the first embodiment, by opening or closing the
valves 21, 23, the liquid level of the ink 4 within the second ink
tank 14 can be controlled to be at the height position of the
opening of the nozzle 1.
In configuration of this embodiment of an amount of the ink 4
within the circulating path is carried out for the flow rate to be
defined by:
TABLE-US-00001 { channel resistance of a path from the main tank 15
through the fourth ink channel 13d, the valve 21, the third ink
channel 13c to the second ink tank 14, and a difference between the
"energy per unit volume" of the ink 4 within the main tank 15 and
the "energy per unit volume" of the ink 4 within the second ink
tank 14 }.
Decreasing of an amount of the ink 4 within the circulating path is
carried out for the flow rate to be defined by:
TABLE-US-00002 { channel resistance of a path from the main tank 15
through the fourth ink channel 13d, valve 23, and the fifth ink
channel 22, and the third ink channel 13c and a difference between
the "energy per unit volume" of the ink 4 within the main tank 15
and the "energy per unit volume" P1 of the ink 4 within the first
ink tank 12 }.
Other configurations and actions are the same as those of the first
embodiment. Thus, description thereof is omitted.
[3] THIRD EMBODIMENT
As shown in FIG. 4, as a first pressure source, a first ink tank 12
that contains the ink 4 supplied to a pressure chamber 3 of an ink
jet head 11 and that is opened to the atmosphere has been adopted.
This first ink tank 12 is arranged at a higher position than an
opening of a nozzle 1 of the ink jet head 11. The "energy per unit
volume" P1 generated in the ink 4 of the liquid level of the first
ink tank 12 is only the potential pressure, and is defined
according to a height position of the liquid level of the ink 4
within the first ink tank 12 that is based on the height position
of the opening of the nozzle 1. "P1/(.rho.g)" in FIG. 4 is this
potential head (m).
As a second pressure source, a second ink tank 14 that contains the
ink 4 flowing out from the pressure chamber 3 of the ink jet head
11 and that is opened to the atmosphere has been adopted. This
second ink tank 14 is arranged at a position lower than the opening
of the nozzle 1 of the ink jet head 11. The "energy per unit
volume" P2 generated in the ink 4 within the second ink tank 14 is
only the potential pressure, and is defined according to a height
position of the liquid level of the ink 4 within the second ink
tank 14 that is based on the height position of the opening of the
nozzle 1. "-P2/(.rho.g)" in FIG. 4 is this potential head (m).
In other words, the difference in elevation between the height
position of the opening of the nozzle 1 and the height position of
the liquid level of the ink 4 within the first ink tank 12 is set
in "P1/(.rho.g)"(m) and the difference in elevation between the
height position of the opening of the nozzle 1 and the height
position of the liquid level of the ink 4 within the second ink
tank 14 is set in "-P2/(.rho.g)"(m), thus the same operations as
those of the first embodiment may be achieved.
Other configurations and actions are the same as those of the first
embodiment. Thus, description thereof is omitted.
In addition, in this embodiment, P1 and P2 are generated by opening
both first and second pressure sources to the atmosphere and using
the potential pressure. However, it is also possible to apply the
first embodiment and this third embodiment in combination, wherein
the configuration of the latter is adopted in either one of the
first pressure source or the second pressure source, while the
former is applied to the other.
[4] FOURTH EMBODIMENT
As shown in FIG. 5, as a first pressure source, a first ink tank 31
that contains the ink 4 supplied to a pressure chamber 3 of an ink
jet head 11 and that is opened to the atmosphere has been provided.
A height position of the liquid level of the ink 4 within this
first ink tank 31 (relative height to the first ink tank 31) is
detected by the first liquid level sensor 35 installed in the first
ink tank 31. The detection result of this first liquid level sensor
35 is supplied to CPU 30. CPU 30 controls a pump 36 to have the ink
4 enter and leave between an ink tank (not shown) and the first ink
tank 31, thereby increasing or decreasing the amount of the ink 4
within the first ink tank 31, so that a height position detected by
the first liquid level sensor 35 will be the same as a
predetermined height position. A first ink channel 39 using a
flexible liquid transport tube is provided between this first ink
tank 31 and an inflow side ink port of the ink jet head 11.
As a second pressure source, a second ink tank 32 that contains ink
4 flowing out from the pressure chamber 3 of the ink jet head 11
and that is opened to the atmosphere is provided. A height position
of this liquid level of the ink 4 within the second ink tank 32
(relative height to the second ink tank 32) is detected by a second
liquid level sensor 37 installed in the second ink tank 32. The
detection result of this second liquid level sensor 37 is supplied
to CPU 30. CPU 30 controls a pump 38 to have the ink 4 enter and
leave between an ink tank (not shown) and the second ink tank 32,
thereby increasing or decreasing the amount of the ink 4 within the
second ink tank 32, so that a height position to be detected by the
second liquid level sensor 37 will be the same as a predetermined
height position. A second ink channel 41 using a flexible liquid
transport tube is provided between this second ink tank 32 and an
outflow side ink port of the ink jet head 11.
Then, a cord 34 is turned over a pulley 33, and the first ink tank
31 and the second ink tank 32 are respectively hung at both ends of
the cord 34. The height position of the first ink tank 31 and that
of the second ink tank 32 change, depending on a rotation position
of the pulley 33.
FIG. 5 shows the condition in which the liquid level of the ink 4
within the first ink tank 31 and that of the ink 4 within the
second ink tank 32 are both lower than the opening of the nozzle 1
by "-Pn/(.rho.g)". Then, the pressure generated in the ink 4 in the
neighborhood of the opening of the nozzle 1 is appropriate pressure
Pn.
Here, the relationship of channel resistance R1 from the first ink
tank 31 to the neighborhood of the nozzle 1 in the pressure chamber
3 and channel resistance R2 from the neighborhood of the nozzle 1
in the pressure chamber 3 to the second ink tank 32 shall be
"R=R2(=R0)".
This is considered as such a situation that, in an ink jet
apparatus in which the ink 4 does not circulate, two sets of
configurations for maintaining the appropriate pressure (negative
pressure) of the ink 4 in the neighborhood of the opening of the
nozzle 1 are juxtaposed by using the potential pressure, and
printing is possible without circulating the ink 4 as it is.
Then, the pulley 33 is turned clockwise as shown in FIG. 6.
When the first ink tank 31 ascends by a distance "Px/(.rho.g)", the
second ink tank 32 descends by "Px/(.rho.g)", which causes a stream
of the ink 4 within the pressure chamber 3 of the ink jet head 11.
Then, the ink flow rate Q is expressed as "Q=Px/R0" by using the
R0(=R1=R2).
Loss (Pa) of the "energy per unit volume" due to the channel
resistance from the first ink tank 31 to the neighborhood of the
nozzle 1 in the pressure chamber 3 is expressed by "R0Q" and is
equal to the increase Px in the "energy per unit volume" P1 of the
ink 4 within the first ink tank 31 that results from the ascent of
the first ink tank 31 by the distance of "Px/(.rho.g)". In
addition, the loss (Pa) of the "energy per unit volume" due to the
channel resistance from the vicinity of the nozzle 1 in the
pressure chamber 3 to the second ink tank 32 is expressed by "R0Q",
and is equal to the decrease Px in the "energy per unit volume" P2
of the ink 4 within the second tank 32 that results from the
descent of the second ink tank 32 by the distance of
"Px/(.rho.g)".
Therefore, the pressure of the ink 4 in the neighborhood of the
opening of the nozzle 1 remains unchanged and the appropriate
pressure Pn is maintained.
Although the ink flow rate Q can be adjusted by a rotation position
of the pulley 33, the pressure of the ink 4 in the neighborhood of
the opening of the nozzle 1 does not fluctuate even during or after
adjustment thereof. That is, the pressure of the ink 4 in the
neighborhood of the opening of the nozzle 1 is not associated with
the ink flow rate Q, and is always kept at the appropriate pressure
Pn.
The case in which the relationship of the channel resistances R1,
R2 is "R1=R2(=R0)" has been described as an example. However, if
the proportion of the channel resistances R1, R2 is "1:r", an
elevating mechanism that provides a proportion "1:r" of the ascent
distance of the first ink tank 31 and the descent distance of the
second ink tank 32 may be used in place of the pulley 33.
[5] FIFTH EMBODIMENT
As shown in FIG. 7, a plurality of ink jet heads 51, 52, 53, 54,
55, 56 of ink circulating type are arranged almost horizontally at
the same height positions as each other. The basic configuration of
these ink jet heads 51 to 56 is identical to the ink jet head 11 as
shown in FIG. 1. However, each of the ink jet heads 51 to 56 has
636 pressure chambers, and each pressure chamber 3 is communicated
to one nozzle each respectively. These 636 pressure chambers and
nozzles 1 are arranged in a direction (depth direction of FIG. 1)
orthogonal to the flow direction of the ink 4 in the respective
pressure chambers 3.
The ink ejection capability of each of the ink jet heads 51 to 56
is 0.167 (mL/sec) per one head, namely, 636 nozzles. In addition,
each pressure chamber 3 in the ink jet heads 51 to 56 has the
perimeter of cross section of 7.6.times.10.sup.-4 (m), and the
cross-section area of 2.4.times.10.sup.-8 (m.sup.2).
As first pressure sources, an upstream side ink tank 58 that
contains the ink 4 to supply to the ink jet heads 51 to 56, and a
positive pressure air tank 65 communicated to a space area of the
upstream side ink tank 58 via an air pipe 76 are provided. The
upstream side ink tank 58 generates the "energy per unit volume" P1
in the ink 4 therein. This "energy per unit volume" P1 is
determined by a height position of the liquid level of the ink 4
within the upstream side ink tank 58 and magnitude of air pressure
PS1 within the positive pressure air tank 65. The air pipe 76
comprises an air valve 78.
The ink 4 within the upstream side ink tank 58 is guided into
respective inflow side ink ports of the ink jet heads 51 to 56 by
the first ink channel 57. The guided ink 4, running through the
respective pressure chambers 3 of the ink jet heads 51 to 56, flows
out from the outflow side ink ports to the second ink channel 59.
The ink 4 outflowed to the second ink channel 59 is guided to the
second pressure source.
As second pressure sources, a downstream side ink tank 60 that
contains ink 4 flowing out from the ink jet heads 51 to 56, and a
negative air tank 66 communicated to a space area of the downstream
side ink tank 60 via an air pipe 77 are provided. The downstream
side ink tank 60 generates the "energy per unit volume" P2 in the
ink 4 therein. This "energy per unit volume" P2 is determined by a
height position of the liquid level of the ink 4 within the
downstream side ink tank 60 and magnitude of air pressure PS2
within the negative pressure air tank 66.
The upstream side ink tank 58 and the downstream side ink tank 60
each have a cross-section area of 5 (cm.sup.2), and a volume of 25
(mL).
The first ink channel 57 are formed by a channel (first channel)
57a almost horizontally provided along the direction of arrangement
of the ink jet heads 51 to 56, a plurality of channels (second
channels) 57b that branch from this channel 57a and are
respectively connected to the inflow side ink ports of the ink jet
heads 51 to 56, and a channel (third channel) 57c that extends
downward from the channel 57a and is communicated to the upstream
side ink tank 58.
The second ink channel 59 is formed by a channel (fourth channel)
59a almost horizontally provided along the direction of arrangement
of the ink jet heads 51 to 56, a plurality of channels (fifth
channels) 59b that branch from this channel 59a and are
respectively connected to the outflow side ink ports of the ink jet
heads 51 to 56, and a channel (sixth channel) that extends downward
from the channel 59a and is communicated to the downstream side ink
tank 60. An opening or closing valve 84 is provided in the channel
59c.
A third ink channel 79 is provided between the downstream side ink
tank 60 and the upstream side ink tank 58. In the third ink channel
79, a filter 63 is provided to remove any foreign matter mixed into
ink 4 and a pump 62.
The upstream side ink tank 58, the first ink channel 57, the ink
jet heads 51 to 56, the second ink channel 59, the third ink
channel 79, the pump 62, and the filter 63 form a circulating path
of the ink 4.
In addition, a main tank 61 that contains the ink 4 and that is
opened to the atmosphere is also provided. A fourth ink channel 81
is provided between this main tank 61 and the third ink channel 79
(the side closer to the downstream ink tank 60).
The upstream side ink tank 58 is provided with a first liquid level
sensor 85 for detecting a height position of the liquid level of
the ink 4 therein, while the downstream side ink tank 60 is
provided with a second liquid level sensor 86 for detecting a
height position of the liquid level of the ink 4 therein.
A valve 80 is provided on the side closer to the downstream side
ink tank 60 than the connecting position of the fourth ink channel
81 in the third ink channel 79. Furthermore, the valve 82 is
provided in the fourth ink channel 81.
The "energy per unit volume" of the ink within the main tank 61 is
set to be greater than the "energy per unit volume" of the
circulating ink at the connecting position of the third ink channel
79 and the fourth ink channel 81.
The positive pressure air tank 64 is provided with a first pressure
sensor 67, while the negative pressure air tank 60 is provided with
the second pressure sensor 68. The first pressure sensor 67 detects
air pressure PS1 within the positive air tank 65, while the second
pressure sensor 68 detects air pressure PS2 within the negative air
tank 66.
One end of an air pipe 70 is connected to the positive air tank 65,
while the other end of the air pipe 70 is opened to the atmosphere.
The air pipe 70 is provided with a leak valve 72 for exhaust
ventilation and an air valve 73 for breathing. The leak valve 72 is
provided with an air resistance that limits the velocity of air
when it is opened. One end of the air pipe 71 is connected to the
negative air tank 66, while other end of the air pipe 71 is opened
to the atmosphere. The air pipe 71 is provided with a leak valve 74
for intaking air and an air valve 75 for breathing. The leak valve
is provided with air resistance that limits the velocity of air
when it is opened.
One end of an air pipe 76 is connected to a position between the
leak valve 74 and the air valve 75 in the air pipe 71, while other
end of the air pipe 76 is connected to a position between the leak
valve 72 and the air valve 73 in the air valve 70. Then, the air
pipe 76 is provided with an air pump 69.
The air pump 69 sucks in air on the side of the air pipe 71, and
feeds the sucked air to the side of the air pipe 70. With the
operation of this air pump 69, the operations of the leak valves
72, 74, and the operations of the air valves 73, 75, the number of
gas molecules within the positive pressure air tank 65 and that in
the negative pressure air tank 66 are respectively adjusted.
If it is supposed that the appropriate pressure of the ink 4 in the
neighborhood of the opening of the nozzle 1 is Pn, a height
position of the liquid level of the ink 4 within the upstream side
ink tank 58 and a height position of the liquid level of the ink 4
within the downstream ink tank 60 are both set to a height position
where the potential pressure equal to the appropriate pressure Pn
is generated, namely, the height position of the opening of the
nozzle 1 (as Pn is a negative value, -Pn/(.rho.g) is a positive
value).
The upstream side ink tank 58 works as a pressure source of the
"energy per unit volume" P1. In this case, the "energy per unit
volume" P1 is expressed by the following formula (8): P1=Pn+PS1
(8)
If this formula (8) is solved for the air pressure PS1 within the
positive pressure air tank 65, the following formula (9) can be
obtained: PS1=P1-Pn (9)
The downstream side ink tank 60 works as a pressure source of the
"energy per unit volume" P2. In this case, the "energy per unit
volume" P2 is expressed by the following formula (10): P2=Pn+PS2
(10)
If this formula (10) is solved for the air pressure PS2 within the
negative pressure air tank 66, the following formula (11) can be
obtained: PS2=P2-Pn (11)
Here, to keep the pressure of the ink 4 in the neighborhood of the
opening of the nozzle 1 at the appropriate pressures Pn, a
relationship of the air pressure PS1 and PS2 may be maintained as
shown in the following formula (12), by using the formula (5)
described in the first embodiment and the formulas (9), (11):
.times..times..times..times..times..times..times..times..times..times..ti-
mes..times..times..times. ##EQU00003##
In other words, CPU 50 may increase or decrease either the number
of gas molecules within the positive pressure air tank 65 or that
in the negative pressure air tank 66, or both so that pressure PS1
detected by the first pressure sensor and pressure PS2 detected by
the second pressure sensor are consistent with the formula
(12).
However, the r represents the proportion of the channel resistance
of the ink 4 from the upstream side ink tank 58 to the neighborhood
of the nozzle 1 in each pressure chamber 3 and the channel
resistance of the ink 4 from the neighborhood of the nozzle 1 in
each pressure chamber 3 to the downstream ink tank 60.
In this fifth embodiment, the channels 57c, 57a, 59c, 59a are
shared by a plurality of ink jet heads 51 to 56. The channel
resistance in these shared parts is considered being proportionally
allotted when the channel resistance of the ink 4 from the upstream
ink tank 58 to the neighborhood of the nozzle 1 of each pressure
chamber 3 and the channel resistance of the ink 4 from the
neighborhood of the nozzle 1 in each pressure chamber 3 to the
downstream side ink tank 60 are calculated. In addition, generally,
channel parts shared by a plurality of pressure chambers 3 also
exist in the inside of respective ink jet heads 51 to 56. The same
also applies to these shared parts, and they are considered being
proportionally allotted to respective pressure chambers 3. A method
of proportional allotment later will be described.
In the case of r=1, in particular, the formula (12) is further
simplified to formula (13): PS2=-PS1 (13)
In other words, in this case, CPU 50 may increase or decrease
either the number of gas molecules within the positive pressure air
tank 65 or that in the negative pressure air tank 66, or both, so
that pressure PS1 detected by the first pressure sensor 67 and
pressure PS2 detected by the second pressure sensor 68 have the
same magnitude but the reverse sign.
On the one hand, the total circulation flow rate of the ink 4
flowing through the circulating path can be adjusted by increasing
or decreasing the difference between detected pressure PS1 and
detected pressure PS2. In other words, if the difference between
the detected pressure PS1 and the detected pressure PS2 is large,
the total circulation flow rate increases. If the difference
between the detected pressure PS1 and detected pressure PS2 is
small, the total circulation flow decreases. In this embodiment, by
using tabular calculation, the total circulation flow rate of the
ink 4 running through the circulating path is adjusted so as to be
a desired value. A method of this adjustment will be described
later.
For the upstream side ink tank 58, the downstream side ink tank 60
and the periphery thereof, a radiator 64 and a cooling fan 83 are
provided. This radiator 64 and the cooling fan 83 cools the
upstream side ink tank 58, the downstream side ink tank 60, and the
periphery thereof.
FIG. 11 shows a specific configuration of the first ink channel 57
and the second ink channel 59.
The ink 4 to be used has a viscosity of 10 (mPasec), and specific
gravity of 0.85. In other words, density .rho. is 850
(kg/m.sup.3).
The channels 57a, 59a that are almost horizontally arranged are
flat tubes having internal dimensions of 3.times.10 (mm), for
example, and length of 55 (mm) between one of the branching points
with the respective channels 57b, 57c, 59b, 59c and its adjacent
branching point. The respective branching channels 57b, 59b are
thin, flexible tubes having an inside diameter of 3 (mm). The
channels 57c, 59c that extend almost vertically are thick circular
tubes having a length of 250 (mm) and inside diameter of 4
(mm).
Suppose that the channel resistance from each channel 57b and each
channel 57b thereof to the neighborhood of each nozzle of the ink
jet heads 51 to 56 is R1, the channel resistance between respective
branching points in the channel is R2, and the channel resistance
of the channel 57c is R3. The channel resistance in the channel
from the neighborhood of the nozzle 1 in each pressure chamber 3 of
the ink jet heads 51 to 56 to each channel 59b, and in each channel
59b thereof is R1, the channel resistance between respective
branching points of the channel 59a is R2, and the channel
resistance of the channel 59c is R3.
These channel resistances are "R1=R1'=1.67.times.10.sup.9
(Pasec/m.sup.3)", "R2=R2'=3.01.times.10.sup.7 (Pasec/m.sup.3)", and
"R3=R3'=3.98.times.10.sup.8 (Pasec/m.sup.3)". At this time, the
proportion of the channel resistance of the ink 4 at the upstream
side from the neighborhood of each nozzle 1 of the ink jet heads 51
to 56 to the ink 4 in the upstream, and the channel resistance of
the ink 4 from the neighborhood of each nozzle 1 of the ink jet
heads 51 to 56 to the ink 4 in the downstream is "1:1". In other
words, now the channel resistance ratio is r=1.
The thickness and shape of the ink channels 57, 59 are selected
based on the concept below. If a thin circular tube is used for the
ink channels 57, 59, the thin circular tube is easily affected by
ink ejection flow because the channel resistance of the ink
channels 57, 59 is high, which thus adversely affects the ejection
performance or stability of the ink 4 from the ink jet heads 51 to
56. On the contrary, if a thicker circular tube is used for the ink
channels 57, 59, air bubbles tend to be left at some locations in
each channel when ink 4 is filled. In addition, if the ink channels
57, 59 are too thick, it would physically be difficult to locate
them. Thus, in view of these points, the shape and thickness of the
ink channels 57, 58 are varied depending on the location.
The channels 57a, 59a that adopt flat tubes suppress channel
resistance by being wider, while making it difficult for air
bubbles to remain in the upper part by making the height 3
(mm).
The channels 57c, 59c that extend vertically have adopted a thicker
circular tube having an inside diameter of 4 (mm), to let air
bubbles float to the upper part. The floating air bubbles may be
sucked out by providing an air bubble blowdown valve (not shown) in
the uppermost part of the channels 57c, 59c, and connecting a
syringe or the like to the air bubble blowdown valve.
Alternatively, the floating air bubbles in the upper part may be
shrunken to the extent that the channel resistance will not be
affected, by selecting an appropriate filling procedure when ink is
filled, or ink feed rate condition. Air bubbles in the upper part
of the channel 57c that has adopted the circular tube may be
discharged from the nozzles 1 of the ink jet heads 51 to 56, by
flowing them away with the ink 4 from the channel 57c that has
adopted the flat tube to the ink jet heads 51 to 56.
On the one hand, the respective channels 57b, 59b are independent
channels for each of ink jet heads 51 to 56. As the flow rate is
small, some channel resistance may exist. Thus, with the higher
priority given to how easily the ink 4 can be filled, that is, how
easily air bubbles can be eliminated, rather than channel
resistance, a thinner tube having an inside diameter of 3 (mm) has
been used so that air bubbles can be carried away with the ink in
the direction in which the ink runs. In such a configuration, the
total circulation flow rate of the ink 4 is set to
1.times.10.sup.-5 (m.sup.3/sec).
The appropriate pressure Pn is -1300 (Pa), for example. Thus, the
liquid level of the ink 4 within the upstream side ink tank 58 and
that within the downstream side ink tank 60 are adjusted such that
they are simply "-Pn/(.rho.g)", that is, 156 (mm) under the opening
of each nozzle 1.
In FIG. 7, the combined channel resistance from the connecting
point of the channels 59b, 57b for the ink jet heads 52 in the
channels 59a, 57a to the ink channels shown left in the figure
(including ink channels 59a, 59b, 57a, 57b to be connected to the
ink jet 51 and the ink jet head 51) is Rt1. In FIG. 8, parts
corresponding to this combined channel resistance Rt1 are shown by
heavy lines. In addition, the channel resistance from the
connecting points of the channels 59b, 57b for the ink jet head 53
in the channels 59a, 57a to the ink channels shown left in the
figure (including the ink channels 52a, 59b, 57a, 57b to be
connected to the ink jet heads 51, 51 and the ink jet heads 51, 52)
is Rt2. In FIG. 9, parts corresponding to this combined channel
resistance Rt2 are shown in heavy lines. Similarly, the channel
resistance from the connecting points of the channels 59b, 57b for
the ink jet head 54 in the channels 59a, 57a to the ink channels
shown at left in the figure (including the ink channels 59a, 59b,
57a, 57b to be connected to the ink jet heads 51, 51, 52, 53 and
the ink jet heads 51, 52, and 53) is Rt3. The channel resistance
from the connecting points of the channels 59b, 57b for the ink jet
head 55 in the channels 59a, 57a to the ink channels shown at left
in the figure (including the ink channels 59a, 59b, 57a, 57b to be
connected to the ink jet heads 51, 52, 53, 54 and the ink jet heads
51, 52, 53, 54) is Rt4. The channel resistance from the connecting
points in the channels 59b, 57 for the ink jet head 56 in the
channels 59a, 57a to the ink channels shown at left in the figure
(including the ink channels 59a, 59b, 57a, 57b to be connected to
the ink jet heads 51, 52, 53, 54, 55 and the ink jet heads 51, 52,
53, 54, 55) is Rt5. In addition, the combined channel resistance
from the upstream side ink tank 58 and the downstream side ink tank
60 to the ink channel 59, the ink channel 57, and the ink jet heads
51 to 56 inclusive is Rt6. In FIG. 10, parts corresponding to this
combined channel resistance Rt6 are shown in heavy lines.
The flow rate of the ink flowing from the channel 57a to the ink
jet head 51 is Q1, the flow rate of the ink flowing from the
channel 57a to the ink jet heads 51, 52 is Q2, the flow rate of the
ink flowing from the channel 57a to the ink jet heads 51 to 53 is
Q3, the flow rate of the ink flowing from the channel 57a to the
ink jet heads to 51 to 54 is Q4, the flow rate of the ink flowing
from the channel 57a to the ink jet heads 51 to 55 is Q5, and the
flow rate of the ink flowing from the channel 57a to all ink jet
heads 51 to 56 (total circulation flow rate of ink 4) is Q6.
The height of the connecting point of the channel 59b for
respective ink jet heads 51 to 56 in the channel 59a is almost
equal to that of the connecting point of the channel 57b for
respective ink jet heads 51 to 56 in the channel 57a, a pressure
difference Pd1 between the connecting point of the channel 59b for
the ink jet head 51 in the channel 59a and the connecting point of
the channel 57b for the ink jet head 51 in the channel 57a is Pd1,
a pressure difference between the connecting point of the channel
59b for the ink jet head 52 in the channel 59a and the connecting
point of the channel 57b for the ink jet head 52 in the channel 57a
is Pd2, a pressure difference between the connecting point of the
channel 59b for the ink jet head 53 in the channel 59a and the
connecting point of the channel 57b for the ink jet head 53 in the
channel 57a is Pd3, a pressure difference between the connecting
point of the channel 59b for the ink jet head 54 in the channel 59a
and the connecting point of the channel 57b for the ink jet head 54
in the channel 57a is Pd4, a pressure difference between the
connecting point of the channel 59b for the ink jet head 55 in the
channel 59a and the connecting point of the channel 57b for the ink
jet head 55 in the channel 57 is Pd5, and a pressure difference
between the connecting point of the channel 59b for the ink jet
head 56 in the channel 59a and the connecting point of the channel
57b for the ink jet head 56 in the channel 57a is Pd6. In addition,
a difference between the "energy per unit volume" P1 of the ink 4
within the upstream side ink tank 58 and the "energy per unit
volume" P2 of the ink 4 within the downstream side ink tank 60 is
Pd7.
The ink flow rate in the ink jet head 51 is Qh1, the ink flow rate
in the ink jet head 52 is Qh2, the ink flow rate in the ink jet
head 53 is Qh3, the ink flow rate in the ink jet head 54 is Qh4,
the ink flow rate in the ink jet head 55 is Qh5, and the ink flow
rate in the ink jet head 56 is Qh6.
A table calculation sheet into which the values of the channel
resistances Rt1 to Rt6 that were calculated from the values of R1,
R1', R2, R2', R3, R3', and relational expressions of these channel
resistances Rt1 to Rt6 and the ink flow rates Q1 to Q6, pressure
differences Pd1 to Pd7, and ink flow rates Qh1 to Qh6 have been
entered is created. Then, if numeric values are adjusted so that
the total circulation flow rate Q6 of the ink 4 will be
"Q6=1.times.10.sup.-5 (m.sup.3/sec)", this table calculation sheet
will have the value as shown in FIG. 12.
In other words, it is required that the difference Pd7 between the
"energy per unit volume" P1 of the ink 4 within the upstream side
ink tank 58 and the "energy per unit volume" P2 of the ink 4 within
the downstream ink tank 60 be 14993 (Pa).
To make the difference Pd7 of the "energy per unit volume" P1 and
P2 be 14993 (Pa) while satisfying the condition "P2=2(-1300)-P1" of
the formula (4), P1=6196 (Pa), and P2=-8796 (Pa).
Then, PS1=-PS2=7496 (Pa).
When the height position of the liquid level of the ink 4 within
the upstream side ink tank 58 (the height position detected by the
first liquid level sensor 85) is higher than a predetermined height
position, the number of rotations of the pump 62 that feeds the ink
4 to the upstream side ink tank 58 is reduced. When it is lower
than the predetermined height position, the number of rotations is
increased. When the height position of the liquid level of the ink
4 within the upstream side ink tank 58 is the same as the
predetermined height position, the volume of fluid transfer of the
pump 62 corresponds to "1.times.10.sup.-5 (m.sup.3/sec)" that is a
set value of the total circulation flow rate.
The valve 82 is opened when the height position of the liquid level
of the ink 4 within the downstream side ink tank 60 (height
position detected by the second liquid level sensor 86) is lower
than a predetermined height position. This allows the downstream
ink tank 60 to be refilled with ink 4 within the main tank 61. This
refill rate is set to about 5 (mL/sec). This refill rate is
determined depending on the "energy per unit volume" of the ink 4
at the connecting point of the third ink channel 79 and the fourth
ink channel 81, the "energy per unit volume" of the ink 4 within
the main tank 61, and the channel resistance of the fourth ink
channel 81 including the valve 82. Thus, their relationships may be
adjusted so that the refill rate is about 5 (mL/sec).
The response lag from after the second liquid level sensor 86
detects a height position until the valve 82 operates is 0.1 (sec).
The adjustment precision of the liquid level including this
response lag is .+-.5 (mm). Therefore, a potential pressure change
corresponding to this height precision is .+-.42 (Pa), and the
range of this pressure change is sufficiently smaller than the
absolute value of -1300 (Pa), which is the appropriate pressure Pn
of the ink 4 in the neighborhood of the opening of each nozzle.
FIG. 13 shows the operations of the air pump 69, the leak valves
72, 74 and the air valves 73, 74 for adjusting the number of gas
molecules within the positive pressure air tank 65 and that within
the negative air pressure tank 66.
In other words, there are seven behavior patterns, and as any of
these behavior patterns is selectively executed depending on the
detection result of the pressure sensors 67, 68, pressure PS1 of
the positive pressure air tank 65 and pressure P2 of the negative
pressure air tank 66 can be kept at +7496 (Pa) and -7496 (Pa),
respectively. For the pressure PS1 of the positive pressure air
tank 65, control targeting +7496 (Pa) is exercised. For pressure
PS2 of the negative pressure air tank 66, not control directly
targeting -7496 (Pa) but control sequentially targeting "-PS1" with
varying pressure "PS1" is exercised. This prevents the pressure of
the ink 4 in the neighborhood of the opening of each nozzle 1 from
deviating from -1300 (Pa), the appropriate pressure, in the process
in which pressure PS1 of the positive pressure air tank 65 reaches
+7496 (Pa).
In the fifth behavior pattern of FIG. 13, the pump 69 is stopped,
and the positive pressure air tank 65 and the negative pressure air
tank 66 are leaked to the atmosphere, respectively. Until this
condition is reached, the sixth and seventh behavior patterns of
FIG. 13 are executed. In other words, pressure PS1 of the positive
pressure air tank 65 is adjusted for targeting 0 (Pa). With this
adjustment, pressure P2 of the negative pressure air tank 66 is
adjusted to be "-PS1". When leaking of the positive pressure air
tank 65 and the negative pressure air tank 66 are ended, both
pressure PS1 of the positive pressure air tank 65 and pressure PS2
of the negative pressure air tank 66 will be at atmospheric
pressure. Then, -1300 (Pa), the potential pressure, is maintained
at each of nozzles 1 of the ink jet heads 51 to 56. In this
condition, the appropriate pressure Pn can be maintained without
any control. If this condition continues, the meniscus can be
maintained even if the printing apparatus is not energized, and the
curved condition of the meniscus does not change even if a power
outage occurs or when the temperature or barometric pressure
changes. Furthermore, at shutdown, or the like, neither will ink
drip from a nozzle nor air enter. Thus, the normal operation can be
promptly resumed upon the next time power is turned on.
With the control described above, the pressure of the ink 4 in the
neighborhood of the opening of each nozzle 1 of the ink jet heads
51 to 56 can be always maintained at the appropriate pressure Pn,
namely, -1300 (Pa). That is, irrespective of the ink flow rate, the
pressure of the ink 4 in the neighborhood of the opening of each
nozzle 1 can always be maintained at the appropriate pressure
Pn.
(a) A supplemental explanation about the gas volume on the upstream
side and that on the downstream side will be given.
It would be more convenient if the gas volume on the upstream side,
which is the sum of the volume of the air space of the upstream
side ink tank 58, the air pipe 76, and the positive pressure air
tank 65, and the gas volume on the downstream side, which is the
sum of the volume of the air space of the downstream side ink tank
60, the air pipe 77, and the negative pressure air tank 66 are set
to be equal. If the air pump 69 is actuated with the first behavior
pattern of FIG. 13 after being opened to the atmosphere with the
fifth behavior pattern of FIG. 13, even while the air pump is being
actuated, or after its actuation ends, an increase in the number of
gas molecules on the upstream side is always equal to a decrease in
the number of gas molecules on the downstream side, and the volume
remains unchanged. Thus, if the gas volume on the upstream side and
that on the downstream side are set equal, simply by actuating the
air pump 69, the ink can be circulated while maintaining the
condition of PS2=-PS1 of the formula (13), even without control by
using the first pressure sensor 67 and the second pressure sensor
68. When the air pump 69 is reversed, the circulation flow rate can
be reduced and circulation can even be stopped while maintaining
the condition PS2=-PS1 of the formula (13). Therefore, if the gas
volume on the upstream side and that on the downstream side are set
equal, other behavior patterns in FIG. 13, namely, use of the
second, third, fourth, sixth, and seventh behavior patterns can be
limited to operations in the case that a slight unbalance, due to
air leak from respective connections, or the like, is corrected.
Thus, the frequency of switching patterns can be reduced, thereby
improving the reliability of the system. Alternatively, if such a
use is possible that air leak from respective parts can be ignored
during a period from opening to the atmosphere with the fifth
behavior pattern to next opening to the atmosphere with the fifth
behavior pattern, the second, third, fourth, sixth and seventh
behavior patterns of FIG. 13 can be omitted. In this case, the air
valves 73 and 75 can be omitted, and the first pressure sensor 67
and the second pressure sensor 68 may be those of lower precision,
or either of them may be omitted, or measurement of a differential
pressure between the positive pressure air tank 65 and the negative
pressure air tank 66 can replace, and the apparatus can be made
simpler and cheaper. As the channel resistance ratio is r=1 in this
embodiment, "it would be more convenient if the gas volume on the
upstream side and gas volume on the downstream side are set equal".
However, when the channel resistance ratio of the upstream and
downstream sides is "1:r", in general, similar effects to the above
description could be obtained if the proportion of the gas volume
on the upstream side and that on the down stream side has been set
to r:1. In addition, in this embodiment, the initial state is open
to the atmosphere, namely, PS1=PS2=0. However, even when the
initial state is PS1=PS2=(predetermined value), in general, the
circulation flow rate can be controlled simply by actuating the air
pump 69 and without changing the ink pressure in the neighborhood
of the nozzle opening, if the proportion of the gas volume on the
upstream side to that on the downstream side has been set to r:1.
This technique can also be applied to any case other than when the
liquid level height positions in the upstream side ink tank 58 and
the downstream side ink tank 60 are set lower than the opening
height position of the nozzle 1, by "-Pn/(.rho.g)".
(b) The ink flow rate in each ink jet head will be explained
next.
When the total circulation flow rate of the ink 4 is
1.times.10.sup.-5 (m.sup.3/sec), simply refer to the table
calculation sheet of FIG. 12 in order to obtain the values of the
ink flow rates Qh1 to Qh6 in each of the ink jet heads 51 to
56.
According to the table calculation sheet of FIG. 12, although the
values of the ink flow rates Qh1 to Qh6 fluctuate between
1.50.times.10.sup.-6 (m.sup.3/sec) to 1.93.times.10.sup.-6
(m.sup.3/sec), the fluctuations, as far as they are in this range,
do not pose any problem because the total circulation flow rate of
the ink 4 does not directly affect the ejection operation of the
ink 4. As a practical matter, with this idea, print results were
compared by changing the ink flow rate Q in the range from 0
(m.sup.3/sec) to 1.93.times.10.sup.-6 (m.sup.3/sec), but no
differences in the print result could be distinguished.
(c) The dynamic pressure in the pressure chambers of respective ink
jet heads will now be explained.
As described above, each pressure chamber 3 of the ink jet heads 51
to 56 has 636 nozzles 1. The pressure chamber 3 has a cross section
area of 2.4.times.10.sup.-8 (m.sup.2).
When the circulation amount of the ink 4 for the ink jet heads 51
to 56 is 1.93.times.10.sup.-6 (m.sup.3/sec), the flow rate of the
ink 4 flowing through each pressure chamber 3 of the ink jet heads
51 to 56 is 3.03.times.10.sup.-9 (m.sup.3/sec), and the current
velocity is 0.126 (m/sec). The dynamic pressure resulting from this
current velocity is negligible, such as:
[850(kg/m.sup.3).times.0.126.sup.2(m/sec)]/2=6.7(Pa) and when
compared with the absolute value of -1300 (Pa), which is the
appropriate pressure Pn of the ink 4 in the neighborhood of the
opening of the nozzle 1, it is adequately small and can be ignored.
Alternatively, as described above, the appropriate pressure Pn may
be set higher by the 6.7 (Pa), from the beginning.
(d) a turbulent flow in the pressure chamber of the ink jet head
will be described.
If the Reynolds number Re is calculated, by supposing that the
perimeter of each pressure chamber 3 is 7.6.times.10.sup.-4 (m),
viscosity of the ink 4 is 10 (mPasec), and specific gravity of the
ink 4 is 0.85, and the flow rate of the ink 4 flowing through each
pressure chamber 3 of the ink jet heads 51 to 56 is
3.03.times.10.sup.-9 (m.sup.3/sec):
Re=(4.times.3.03.times.10.sup.-9)/{(0.01/850).times.7.6.times.10.sup.-4}=-
1.36 The value of the Reynolds number Re, 1.36 is adequately small
and allows the possible effect of a turbulent flow to be
ignored.
(e) The temperature control of ink will next be described.
The ink jet heads 51 to 56 generate heat during operation
(printing). According to this heat generation, temperatures of the
ink 4 vary. If temperatures of the ink 4 widely change, it will
affect the ink ejection characteristic. To cope with the
temperature change, the radiator 64 and the cooling fan 83 as
described above are adopted.
FIG. 14 shows specific configurations of the radiator 64 and the
cooling fan 83. The radiator 64 has a heat sink 92 made of
aluminum, and enables heat exchange by thermal resistance of 1
(.degree. C./W) between the heat sink 92 and the outer air. The
upstream side ink tank 58 and the downstream side ink tank 60 are
attached to the heat sink 92. The cooling fan 83 supplies outer air
to the heat sink 92, thus cooling the heat sink 92. For example, if
10W, as energy per unit time minus the heat quantity per unit time
the ejected ink deprives of the power consumption of the ink jet
heads 51 to 56, is given to the circulating ink, temperatures of
the ink 4 can be controlled at about +10 (.degree. C.) above the
outer air by this cooling.
In FIG. 9, 90 designates a sheet passage unit through which the
sheet printed by the ink jet heads 51 to 56 passes, and 91 is a
housing in which the ink jet apparatus of the present invention is
contained. As the heat sink 92 is provided in the immediate
proximity of the sidewall of the housing 91, the heat sink 92 can
be directly and efficiently cooled down by outer air.
If an attempt to arrange the upstream side ink tank 58 and the
downstream side ink tank 60 at a location that is equidistant from
each of the ink jet heads 51 to 56 is made, the location is close
to the center of the housing 91. Direct cooling by outer air is
difficult around the center of the housing 91. On the other hand,
in this embodiment, the upstream side ink tank 58 and the
downstream side ink tank 60 are not necessarily arranged at a
location that is equidistant from each of the ink jet heads 51 to
56. That is, if the proportion of the channel resistance on the
upstream side and that on the downstream side has been set so that
it can be "r" for any of the ink jet heads 51 to 56, the pressure
of the ink 4 in the neighborhood of the opening of each nozzle 1 of
the ink jet heads 51 to 56 can be respectively maintained at the
appropriate pressure Pn, and thus the upstream side ink tank 58 and
the downstream side ink tank 60 may be arranged on the end of the
housing 1. Thus, as described above, a configuration can be adopted
wherein the heat sink 92 is provided on the sidewall of the housing
91 and the upstream side ink tank 58, and the downstream side ink
tank 60 may be attached to the heat sink 92.
(f) The maintenance will be explained.
A first maintenance method is not only to increase the "energy per
unit volume" P1 of the ink 4 within the upstream side ink tank 58
to approximately 22000 (Pa) but also to adjust the "energy per unit
volume" P2 of ink 4 within the downstream side ink tank 60 so as to
be "-P1", as the change of the "energy per unit volume" P1. This
enables the circulation amount of the ink 4 to be almost tripled
while the pressure of the ink 4 in the neighborhood of the opening
of each nozzle 1 of the ink jet heads 51 to 56 is still maintained
at -1300 (Pa), the appropriate pressure Pn. As the ink 4
circulates, foreign matter and air bubbles within the ink jet heads
51 to 56 flow to the downstream side ink tank 60. Air bubbles flown
to the downstream side ink tank 60 come up and disappear, foreign
matter flown to the downstream side ink tank 60 is filtered by the
filter 63, and the ink from which air bubbles and foreign matter
were removed is returned to the upstream side ink tank 58. If the
circulation amount of the ink 4 increases, these operations can be
performed more effectively.
A second maintenance method is to change the "energy per unit
volume" P2 of the ink 4 within the downstream side ink tank 60 to
"-P1+.alpha.". With this, the ink 4 is spilt out from respective
nozzles 1 of the ink jet heads 51 to 56. The spilled ink 4 is
sucked up by a suction nozzle or scraped up by a blade. Such
spilling of the ink 4 can remove foreign matter and air bubbles
near the surface of each nozzle 1. If there is any foreign matter
or air bubbles near the surface of each nozzle 1, this second
maintenance method is effective.
A third maintenance method is to close the valve 84
instantaneously. With this, the ink 4 is spilt out from respective
nozzles 1 of the ink jet heads 51 to 56. The spilt ink 4 is sucked
up by a suction nozzle or scraped up by the blade. The speed of the
ink 4 that flows through respective nozzles 1 is faster in the
third maintenance method than in the second maintenance method.
That is, the third maintenance method is more effective for
contamination inside of respective nozzles 1.
However, if the second maintenance method and the third maintenance
method are executed when foreign matter larger than the nozzle 1
lies in the upstream side rather than in the neighborhood of the
nozzle 1 in the pressure chamber 3, the foreign matter may be
jammed into the nozzle 1. Thus, it would be desirable to execute
the second maintenance method and the third maintenance method,
after the first maintenance method is executed. A fourth
maintenance method takes this into consideration, and is the most
powerful method for removing contamination of each nozzle, and has
the following sequences.
First, similarly to the first maintenance method, the circulation
amount of the ink 4 is increased. Then, similarly to the second
maintenance method, the nozzle pressure is shifted slightly to the
positive pressure side to cause a tiny amount of the ink 4 to spill
from each nozzle 1. In this condition, similarly to the third
maintenance method, the valve 84 in the channel 59c is
instantaneously closed to cause the ink 4 to be spilled rapidly.
Then, after returning the valve 84 to the open state, the ink 4
spilled from each nozzle 1 is sucked up by the suction nozzle or
scraped up by the blade. Then, after returning the "energy per unit
volume" P2 of ink 4 within the downstream side ink tank 60 to
"-P1", the ink 4 remaining around each nozzle 1 may be sucked up by
the suction nozzle or scraped up by the blade again. Finally, the
circulation amount of the ink 4 is returned to normal.
The procedure described herein is not limited to the case in which
maintenance of the ink jet apparatus is done, and may be used as a
method of washing when the head is washed by using cleaning
fluid.
In that case, a washing method can be provided that uses less
cleaning fluid and is free from the risk that foreign matter is
jammed into the nozzle 1.
(g) The filling of the ink 4 will be explained.
A method of filling the ink 4 in the ink jet heads 51 to 56, the
ink channels 57, 59, 79, the upstream side ink tank 58 and the
downstream side ink tank 60 from initial empty state will be
described next. It is assumed as an initial condition that the main
tank 61 contains sufficient ink 4, and either of the positive
pressure air tank 65 and the negative pressure air tank 66 is
opened to the atmosphere.
The valve 80 is closed, the valve 82 is opened, and the pump 62 is
driven at a predetermined number of rotations. With this, the ink 4
within the main tank 61 is supplied to the upstream side ink tank
58. The air valve 78 and the valve 84 are opened.
When the ink 4 in the upstream side ink tank 58 increases and the
height position of the liquid level of the ink 4 (the height
position detected by the first liquid level sensor 85) reaches a
predetermined height position, the air valve 78 is closed. When the
air valve 78 is closed, the ink 4 in the upstream side ink tank 58
ascends through the channel 57c and flows into the channel 57a. The
ink 4 that flows into the channel 57a runs through each channel
57b, and flows into each pressure chamber 3 of the ink jet heads 51
to 56. Then, it is guided from each pressure chamber 3 through each
channel 59b, the channel 59a, and the channel 59c into the
downstream side ink tank 60.
At the time, if the flow rate of the ink 4 is too high, much of the
ink 4 leaks from respective nozzles 1 of the ink jet heads 51 to
56, whereas if the flow rate of the ink 4 is low, filling takes
more time. Thus, the flow rate of the ink 4 is set to an
appropriate value so that such inconveniences will not occur. In
addition, if the ink jet heads 51 to 56 are capped and air
tightness of respective nozzles 1 is maintained, the amount of the
ink 4 that will spill from respective nozzles 1 can be reduced.
Alternatively, if cleaning is done in advance so that there is no
liquid or foreign matter around respective nozzles 1 of the ink jet
heads 51 to 56, the flow rate at which the ink 4 starts to spill
from respective nozzles 1 (at a flow rate of the ink 4 causing
spilling of the ink 4 from the respective nozzles when the flow
rate of the ink 4 is increased) can be increased. If the edge of a
nozzle opening is wet with the ink or there is any foreign matter
at the edge of the opening, the ink will freely spread to the
outside of the nozzle opening, even if it is a minimal positive
pressure. In contrast, if the edge of the nozzle opening is dry,
the ink can form a convex droplet at the nozzle opening. In this
case, even if the flow rate during filling is high, resulting in a
positive pressure in the neighborhood of the nozzle opening, the
ink will not spill from the nozzle if the value falls within the
positive pressures that can be balanced with the pressure due to
surface tension of the droplet. Therefore, it is desirable to clean
in advance the periphery of the respective nozzles 1 by a wipe
operation, or the like.
If the height position of the liquid level of the ink 4 (height
position detected by the second liquid level sensor 86) within the
downstream side ink tank 60 reaches a predetermined height
position, the air valve 78 and the valve 80 are opened, and the
valve 82 is closed. Then, the air pump is started, and then a
normal circulating behavior of the ink 4 occurs.
So far, a method of filling by using the air bubbles is described.
However, there is some filling method without using the air valve
78. In the following, a method of filling without using the air
valve 78 is described.
The valve 80 is closed, the valve 82 is opened, and the pump 62 is
driven at predetermined number of rotations. With this, the ink 4
within the main tank 61 is supplied to the upstream side ink tank
58.
When the ink 4 within the upstream side ink tank 58 increases, and
the height position of the liquid level of the ink 4 (height
position detected by the first liquid level sensor 85) reaches a
predetermined height position, the pump 62 is controlled so that
the condition can be maintained. For example, when the height
position of the liquid level of the ink 4 within the upstream side
ink tank 58 is higher than the predetermined height position, the
pump 62 is stopped. If the height position of the liquid level of
the ink 4 within the upstream side ink tank 58 is lower than the
predetermined height position, the pump 62 is driven at a
predetermined number of rotations.
With this control, pressure PS1 of the positive pressure air tank
65 is increased. For the ink 4 to pass through the highest point in
the ink channel 57, it becomes essential that the pressure PS1 of
the positive pressure air tank 65 be higher than potential pressure
of true height difference between the highest point in the ink
channel 57 and the liquid level of the ink 4 within the upstream
ink tank 58. When the ink 4 goes over the highest point in the ink
channel 59 after passing through respective pressure chambers 3 of
the ink jet heads 51 to 56, it is also a mandatory requirement that
the pressure PS1 of the positive pressure air tank 65 be higher
than the potential pressure of the true height difference between
the highest point in the ink channel 59 and the liquid level of the
ink 4 within the upstream ink tank 58.
However, if the pressure PS1 of the positive pressure air tank 65
is too high, a considerable amount of the ink 4 will leak from
respective nozzles 1 of the ink jet heads 51 to 56. If the pressure
PS1 of the positive pressure air tank 65 is low, filling takes too
much time. Thus, the pressure PS1 of the positive pressure air tank
65 is set to an appropriate value that will not cause such
inconveniences.
First, the pressure PS1 of the positive pressure air tank 65 may be
increased. Then, by judging the time that the ink 4 goes beyond the
highest point of the ink channel 57 or the highest point in the ink
channel 59, the pressure PS1 of the positive pressure air tank 65
may be decreased. In addition, if the ink jet heads 51 to 56 are
capped and air tightness of respective nozzles 1 is maintained, the
amount of the ink 4 that will spill from respective nozzles 1 can
be reduced. Alternatively, if cleaning is done in advance so that
there is no liquid or foreign matter around respective nozzles 1 of
the ink jet heads 51 to 56, the pressure of the positive pressure
air tank 65 from which the ink 4 starts to spill from respective
nozzles 1 (a value of a positive pressure causing spilling of the
ink 4 from the respective nozzles when a pressure of the positive
pressure air tank 65 is increased) can be increased.
If the height position of the liquid level of the ink 4 (height
position detected by the second liquid level sensor 86) within the
downstream side ink tank 60 reaches a predetermined height
position, the valve 80 is opened, and the valve 82 is closed. Then,
pressure PS2 of the negative air tank 66 is controlled to "-PS1",
and the "energy per unit voltage" P1 of the ink 4 within the
upstream side ink tank 58 is set to a normal value. Then, the
normal circulating behavior of the ink 4 occurs.
If the time when operation shifts to the normal circulation control
of the ink 4 is set earlier than the time when the height position
of the liquid level of the ink 4 within the downstream side ink
tank 60 reaches the predetermined height position, the amount of
the ink 4 that will spill from respective nozzles 1 can be reduced.
To implement this, another liquid level sensor may be provided
below the second liquid level sensor 86. Alternatively, based on
either the start time of the filling operation or the time when the
upstream side ink tank 58 detects the liquid level, or both, it can
be estimated and judged when the ink 4 starts to accumulate within
the downstream side ink tank 60, and a shift to the normal
circulation control may be made when the time is reached.
[6] SIXTH EMBODIMENT
As shown in FIG. 15, the ink channels 91, 92 and the pumps 87, 88
have been adopted in place of the third ink channel 79, the fourth
ink channel 81, the valves 80, 82, the pump 62, and the filter 63
of FIG. 7.
The ink channel 91 guides the ink 4 within the main tank 61 to the
upstream side ink tank 58. The pump 87 is provided in this ink
channel 91. Controlled by CPU 50, the pump 87 increases or
decreases the amount of the ink 4 within the upstream side ink tank
58 so that a height position detected by the first liquid level
sensor 85 (height position of the liquid level of the ink 4 within
the upstream ink tank 58) is the same as the predetermined height
position.
The ink channel 92 guides the ink 4 within the main tank 61 to the
downstream side ink tank 60. The pump 88 is provided in this ink
channel 92. Controlled by CPU 50, the pump 88 increases or
decreases the amount of the ink 4 within the downstream side ink
tank 60 so that a height position to be detected by the second
liquid level sensor 86 (height position of the liquid level of the
ink in the downstream ink tank 60) is the same as the predetermined
height position.
This case has the advantage that control becomes easier although
the number of pumps increases.
Here, the embodiment in which the filter is omitted has been
described. However, for the purpose similar to that of the filter
63, a filter may be provided in the ink channel 91.
Other configurations and actions are the same as those of the fifth
embodiment. Therefore, description thereof is omitted.
[7] SEVENTH EMBODIMENT
It is desirable that an ink channel has the capability of
preventing air bubbles from being mixed, and that of eliminating
any mixed air bubbles. This is because once air bubbles are fed to
the ink jet heads, some of the air bubbles may enter the pressure
chambers, which, as a result, may cause such problems as generation
of ink ejection pressure by the actuator being inhibited by air
bubbles, ink not being ejected from the nozzles, print quality
being deteriorated, or the like. Thus, it is desirable to take the
measures described below at ink inflow ports of the upstream side
ink tank 58 and the downstream side ink tank 60 in order to prevent
air bubbles from getting mixed into ink channels as much as
possible.
The ink 4 that can flow into the upstream side ink tank 58 and the
downstream side ink tank 60 has current velocity. Even if air
bubbles are mixed in this ink 4, they come up to the liquid level
of the ink 4 within the ink tanks 58, 60, disappear, and do not
flow into the channels 57c, 79, if the current velocity of the ink
4 is sufficiently small. However, in the case in which air bubbles
are mixed into the ink 4, the current velocity of the ink 4 is high
to some extent, and yet air bubbles are small, the buoyancy of air
bubbles is not enough to keep them afloat, and so they sink, and
stochastically flow into the channels 57c, 79.
Even if a flow direction of the ink 4 that flows into the upstream
side ink tank 58 and the downstream side ink tank 60 is upward or
sideways, the ink will finally impinge against the wall surface of
each ink tank, swirl around in the ink tanks, and finally
stochastically flow into the channels 57c, 79 if the current
velocity of the ink 4 is fast enough.
In the ink jet heads of the ink circulating type, in particular, as
the current velocity of the ink 4 is fast, such a problem tends to
occur. To prevent this, the current velocity of the ink 4 flowing
into the upstream side ink tank 58 and the downstream side ink tank
60 may be decelerated. To decelerate the current velocity of the
ink 4 flowing into the upstream side ink tank 58 and the downstream
side ink tank 60 while maintaining the necessary flow rate, the
cross section area of the flow on the side into which each ink
flows may be increased.
Thus, as shown in FIG. 16, a cylinder 93 is erectly provided as a
first decelerating mechanism inside of the upstream ink tank 58.
This cylinder 93 divides the interior of the upstream side ink tank
58 into 2 areas. Into the inner area of this cylinder 93 is
introduced an outlet of the third ink channel 79 is provided in the
inner area of this cylinder 93. The diameter of the cylinder 93 is
sufficiently larger than that of the outlet of the third ink
channel 79, and set three times larger, for example.
More specifically, the cylinder 93 is a small chamber with the
inner area thereof isolated within the upstream side ink tank 58,
and is structured to have the ink 4 flowing into the inner area
spill over the upper edge (longer than the perimeter of the outlet
opening in the third ink channel 79).
The ink 4 flowing into the upstream side ink tank 58 from the third
ink channel 79 first enters the cylinder 93. The liquid level of
the ink that entered the cylinder 93 rises, running over the top
opening (the upper edge) of the cylinder 93 in due time and falling
into the outer area of the cylinder 93. As the opening of the
cylinder 93 is provided in the top, the ink 4 is then flowing
upwards or sideways. Furthermore, the current velocity of the ink 4
is sufficiently low, in accordance with a proportion with the
diameter of the cylinder 93 and that of the outlet of the third ink
channel 79, or a proportion with the perimeter of the cylinder 93
and that of the outflow of the third ink channel 79.
As the current velocity of the entering ink does not have a
downward component and is sufficiently low, even if the ink 4 flow
into with small air bubbles mixed, neither sink nor swirl around,
and instead slowly come up to the liquid level of the ink 4 and
disappear. As the inlet of the channel 57 is provided lower than
the opening of the cylinder 93 in the outer area of the cylinder
93, the chance of air bubbles running through the channel 57c and
being fed into respective ink jet heads 51 to 56 is very low.
On the one hand, as the side ink in the downward ink tank 60 is not
directly fed to respective ink jet heads 51 to 56, the level f
importance is lower than on the upstream side. However, it is not
preferable that air bubbles flow into the third ink channel 79,
because flowing into the third channel 79, the air bubbles
accumulate in the pump or filter, or pass through the pump or
filter, though the chance is low, and return to the upstream tank,
therefore circulating in the circulating path if the air bubbles
flow into the third channel 79. Thus, as with the case of the
upstream side tank, it is desirable that a decelerating mechanism
is provided in the downstream side ink tank 60, which makes it
difficult to flow into the third ink channel 79.
From the inner bottom to sidewalls of the downstream side ink tank
60, a partition wall 94 is erectly provided as a second
decelerating mechanism. This partition wall 94 separates the
interior of the downstream side ink tank 94 into one area and
another area. The outlet of the ink channel 59c is introduced into
the one area, while the inlet of the third ink channel 79 is
introduced into the other area. The linear length of the upper part
of the partition wall 94 is longer than the perimeter of the outlet
of the ink channel 59c, and set three times longer, for
example.
More specifically, the partition wall 94 is a small cell with the
inner one area thereof isolated within the downstream ink tank 60,
and is structured to have the ink 4 flowing into the inner one area
spill over the upper edge (longer than the perimeter of the inlet
opening in the ink channel 59c).
The ink 4 flowing into the downstream side ink tank 60 from the ink
channel 59c first enters the one area. The liquid level of the ink
that entered the one area rises, running over the top opening (the
upper edge) of the partition wall 94 in due time and falling into
the other area. At this time, the current velocity of the ink 4 is
sufficiently low and the direction thereof is sideways. If air
bubbles are contained in the ink 4 flowing into the one area, they
neither sink nor swirl around, and come up to the liquid level of
the ink 4 and disappear. Therefore, it is almost impossible for air
bubbles to enter the third ink channel 79.
As in this embodiment, if the cylinder 93 or the partition wall 94
is provided, respective ink tanks 58, 60 have two different liquid
levels bounded by the cylinder 93 or the partition wall 94. The
respective ink tanks 58, 60 have liquid level sensors, and we
describe in the following which liquid level within the respective
ink tanks the liquid level sensors should detect, respectively.
As described earlier, the most important thing needed to eject the
ink in a stable manner and with high quality is to keep the
pressure of the ink 4 in the neighborhood of the opening of
respective nozzles 1 at an appropriate value Pn. To this end, the
liquid levels to which channels connecting the upstream side ink
tank 58 and the downstream side ink tank 60 with respective ink jet
heads 51 to 56 are communicated are more important.
More specifically, to correctly control the "energy per unit
volume" P1 of the ink 4 within the upstream side ink tank 58, the
liquid level sensor 85 of the upstream side ink tank 58 detects a
height position of the liquid level of the ink 4 which lies in the
outer area of the cylinder 93 (the side in which the channel 57c
lies). To correctly control the "energy per unit volume" P2 of the
ink 4 within the downstream side ink tank 60, the liquid level
sensor 86 of the downstream side ink tank 60 detects a height
position of the liquid level of the ink 4 which lies in said one
area (the side in which the ink channel 59 lies). If the
decelerating mechanism of the downstream side ink tank 60 is a
cylinder, the liquid level sensor 86 should be provided within the
cylinder surrounded by ink, thus making it difficult to install the
liquid level sensor. Thus, in this embodiment, a partition plate is
used as a decelerating mechanism, which makes it easier to install
an ink liquid level sensor on the side to which the ink is flowing
from the side in which the ink channel 59c lies, namely, the
heads.
Other configurations and actions are the same as those of the first
embodiment. Therefore, description thereof is omitted.
[8] EIGHTH EMBODIMENT
In the first to seventh embodiments, the ink jet head 11 of a
circulating type with the configuration as shown in FIG. 1 is used.
However, the ink jet head for use is not limited to such, and an
ink jet head 100 of a circulating type with the configuration as
shown in FIG. 17 may be used.
More specifically, two openings 101a, 101b are formed on a
substrate 101. A plate 102 is provided on a top surface of the
substrate and in such a manner that it blocks the openings 101a,
101b. The plate 102 has pressure chambers 102c, 102d and ink
ejecting nozzles 102a, 102b in positions corresponding to said
openings 101a, 101b, respectively. In addition, an ink deposit
section 103 is provided on the undersurface side of the substrate
101 into which the ink 110 flows through ink channels 104, 105. The
ink 110 within the ink deposit section 103 is guided through said
openings 101a, 101b into the pressure chambers 102c, 102d and the
nozzles 102a, 102b.
Actuators (heating heaters) 106a, 106b are provided in positions
corresponding to the nozzles 102a, 102b on the top face of the
substrate 101. These actuators 106a, 106b generate heat due to
application of a pulse wave like voltage. This heat generation
causes a phase change in the ink 100. With this phase change, air
bubbles are generated in ink 110. The pressure of the air bubbles
ejects the ink 4 from the nozzles 102a, 102b.
In this configuration, the ink 4 circulates in the path of the ink
channel 104, the ink deposit section 103, and an ink channel 105,
and only the ink 104 to be ejected is fed to the pressure chambers
102c, 102d and the nozzles 102a, 102b via the openings 101a, 101b.
That is, unlike the first to seventh embodiments, the circulation
flow of the ink 4 does not run through the pressure chambers.
The first to seventh embodiments may be carried out by using such
the ink jet head 100, considering the "neighborhood of the nozzle 1
in the pressure chamber 3" described in the first to seventh
embodiments as the "ink deposit section 103" of this embodiment.
More specifically, the channel resistance r represents a proportion
of the channel resistance from the ink deposit section 103 to the
first pressure source and the channel resistance from the ink
deposit section 103 to the second pressure source.
In the configuration, when no ink is ejected or the ink is ejected
only slightly from the nozzles 102a, 102b, the "pressure of ink in
the neighborhood of the openings of the nozzles 102a, 102b" is a
value obtained by adding "the potential pressure attributed to a
slight difference of elevation between the neighborhood of the
nozzle 1 in the pressure chamber 3 and the neighborhood of the
opening of the nozzle 1" to the "pressure of the ink in the ink
deposit section 103".
The relationship among the three components is equal to the
relationship among the "pressure of the ink 4 in the neighborhood
of the opening of the nozzle 1", the "pressure in the neighborhood
of the nozzle 1 in the pressure chamber 3", and the "potential
pressure attributed to a slight difference of elevation between the
neighborhood of the nozzle 1 in the pressure chamber 3 and the
neighborhood of the opening of the nozzle 1".
In addition, it may be considered that when the ink 4 is ejected,
the pressure of the ink in the neighborhood of the opening of the
nozzles 102a, 102b decreases by the pressure obtained by
multiplying the ejection flow rate of the ink 4 by the channel
resistance from the branching points to the nozzles 102a, 102b
through the openings 101a, 101b and the pressure chambers of 102c,
102d.
It is also possible to collectively call the "neighborhood of the
nozzle 1 in the pressure chamber" described in the first to seventh
embodiments and the "ink deposit section 103" of this embodiment as
"the "branching point between the channel communicated from the
first pressure source to the second pressure source via the ink jet
head and the channel communicated to the nozzle".
Furthermore, the ink jet head 100 used in this ink jet apparatus
may be of the type branching in the middle of the circulating path
and through the filter, into the actuators 106a, 106b and the
nozzles 102a, 102b. In this case, the filter may be considered as
the branching point.
As the actuators 106a, 106b, actuators of the piezoelectric type,
piezoelectric share mode type, thermal ink jet type or the like are
also applicable, in addition to those of the heating type.
[9] The proportional allotment of the channel resistance described
in the fifth embodiment will be described.
In the fifth embodiment, the ink channels 57c, 57a, 59c, 59a are
shared by a plurality of ink jet heads 51 to 56. The channel
resistance in these shared parts is allotted to the ink jet heads 1
to 56 when calculating the channel resistance from the upstream
side ink tank 58 to respective nozzles 1 and the channel resistance
from respective nozzles 1 to the downstream side ink tank 60.
In other words, if the ink channels are not separated for each ink
jet head, and have a common ink channel and branching points shared
by the plurality of ink jet heads, it can be considered that the
common ink channels are proportionally allotted at the same rate as
that of respective channel resistances of independent ink channels
to which the shared ink channel branches. Thus, the channel
resistance can be calculated for each jet head, by proportionally
allotting the shared ink channel as parallel resistance having the
same rate as that of each of the channels to which the shared ink
channel branches.
Here, how to allot the shared ink channels to parallel resistance
using an equivalent circuit schematic will be described.
When it is supposed that the channel resistance from the nozzle of
the ink jet head 201 to the upstream side branching point is R3,
the channel resistance from the nozzle of the ink jet head 201 to
the downstream side branching point is R4, the channel resistance
from the nozzle of the ink jet head 202 to the upstream side
branching point is R5, the channel resistance from the nozzle of
the ink jet head 202 to the downstream side branching point is R6,
the channel resistance of the shared ink channels on the upstream
side is R7, and the channel resistance of the shared ink channels
on the downstream side is R8, the channel resistance R7 is
considered to be proportionally allotted to the channel resistance
R71 and the channel resistance R72 that are mutually parallel
connected, and that the channel resistance R8 is considered to be
proportionally allotted to the channel resistance R81 and the
channel resistance R82 that are mutually parallel connected.
A proportional allotment method is to do so such that the following
"R71:R72=R81:R82=(R3+R4):(R5+R6)" "1/R7=1/R71+1/R72"
"1/R8=1/R81+1/R82" conditions are met. At this time,
"R71:R81=R72:R82=R7:R8".
After the proportional allotment, the channel resistance in the
upstream side of the nozzle of the ink jet head 201 shall be
"R71+R3", the channel resistance in the downstream side of the
nozzle of the ink jet head 201 shall be "R81+R4", the channel
resistance in the upstream side of the nozzle of the ink jet head
202 shall be "R72+R5", and the channel resistance in the downstream
side of the nozzle of the ink jet head 202 shall be "R82+R6".
Here, it would be easier to handle if the channel resistances in
each part could meet
"R3:R4=R5:R6=R7:R8=1:r".
Then, "(R71+R3):(R81+R4)=(R72+R5):(R82+R6)=1:r". In other words, if
the proportion of the upstream side channel resistance and the
downstream side channel resistance has been completed to "1:r" in
each of the independent ink channels and the shared ink channels,
it can be stated that the proportion of the upstream side channel
resistance and the downstream side channel resistance viewed from
the nozzles is "1:r" without actually calculating the channel
resistances R71, R72, R81, and R82. The fifth embodiment is made as
such.
Additional advantages and modifications will readily occur to those
skilled in the art. Therefore, the invention in its broader aspects
is not limited to the specific details and representative
embodiments shown and described herein. Accordingly, various
modifications may be made without departing from the spirit or
scope of the general inventive concept as defined by the appended
claims and their equivalents.
* * * * *